MVP get us working fully on nixos

NB: for now this is linking to a presumed local clone of the
`poetry2nix` repo since part of fixing what was adjusted here needs to
be patched upstream, which means hackin on the p2n repo in tandem B)

Since there's some dependency build issues we need
to tweak the following to get baseline `nix develop` working:
- drop `python-levenshtein` (required by `fuzzywuzzy[speedup]`) for now
  since the overlay and/or wheel install needs to be properly figured
  out.
- build `pyqt5` from src for the moment (since `preferWheel` doesn't
  seem to be workin?) despite it taking forever XD
- add in the `flake.lock` file.

flake.nix

@@ -0,0 +1,156 @@
+# NOTE: to convert to a poetry2nix env like this here are the
+# steps:
+# - install poetry in your system nix config
+# - convert the repo to use poetry using `poetry init`:
+#   https://python-poetry.org/docs/basic-usage/#initialising-a-pre-existing-project
+# - then manually ensuring all deps are converted over:
+# - add this file to the repo and commit it
+# - 
+{
+  description = "piker: trading gear for hackers (pkged with poetry2nix)";
+
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  # see https://github.com/nix-community/poetry2nix/tree/master#api
+  inputs.poetry2nix = {
+    url = "github:nix-community/poetry2nix";
+    # url = "github:K900/poetry2nix/qt5-explicit-deps";
+    # url = "/home/lord_fomo/repos/poetry2nix";
+
+    inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+    poetry2nix,
+  }:
+    # TODO: build cross-OS and use the `${system}` var thingy..
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        # use PWD as sources
+        projectDir = ./.;
+        pyproject = ./pyproject.toml;
+        poetrylock = ./poetry.lock;
+
+        # TODO: port to 3.11 and support both versions?
+        python = "python3.10";
+
+        # for more functions and examples.
+        # inherit
+        # (poetry2nix.legacyPackages.${system})
+        # mkPoetryApplication;
+        # pkgs = nixpkgs.legacyPackages.${system};
+
+        pkgs = nixpkgs.legacyPackages.x86_64-linux;
+        lib = pkgs.lib;
+        p2npkgs = poetry2nix.legacyPackages.x86_64-linux;
+
+        # define all pkg overrides per dep, see edgecases.md:
+        # https://github.com/nix-community/poetry2nix/blob/master/docs/edgecases.md
+        # TODO: add these into the json file:
+        # https://github.com/nix-community/poetry2nix/blob/master/overrides/build-systems.json
+        pypkgs-build-requirements = {
+          asyncvnc = [ "setuptools" ];
+          eventkit = [ "setuptools" ];
+          ib-insync = [ "setuptools" "flake8" ];
+          msgspec = [ "setuptools"];
+          tabcompleter = [ "setuptools" ];
+          pdbp = [ "setuptools" ];
+          xonsh = [ "setuptools" ];
+          trio-typing = [ "setuptools" ];
+          trio-util = [ "setuptools" ];
+          tricycle = [ "setuptools" ];
+          tractor = [ "setuptools" ];
+          pyqt6-sip = [ "setuptools" ];
+
+          # don't need these right?
+          # tomlkit = [ "setuptools" ];
+        };
+
+        # auto-generate override entries
+        p2n-overrides = p2npkgs.defaultPoetryOverrides.extend (self: super:
+          builtins.mapAttrs (package: build-requirements:
+            (builtins.getAttr package super).overridePythonAttrs (old: {
+              buildInputs = (
+                old.buildInputs or [ ]
+              ) ++ (
+                builtins.map (
+                  pkg: if builtins.isString pkg then builtins.getAttr pkg super else pkg
+                  ) build-requirements
+              );
+            })
+          ) pypkgs-build-requirements
+        );
+
+      in
+        {
+          # let
+          # devEnv = poetry2nix.mkPoetryEnv {
+          #     projectDir = ./.;
+          # };
+
+          packages = {
+            # piker = poetry2nix.legacyPackages.x86_64-linux.mkPoetryEditablePackage {
+            #   editablePackageSources = { piker = ./piker; };
+            piker = p2npkgs.mkPoetryApplication {
+              projectDir = projectDir;
+
+              # SEE ABOVE for auto-genned input set, override
+              # buncha deps with extras.. like `setuptools` mostly.
+              # TODO: maybe propose a patch to p2n to show that you
+              # can even do this in the edgecases docs?
+              overrides = p2n-overrides.extend(
+                final: prev: {
+
+                  # TODO: get this workin with p2n and nixpkgs..
+                  # pyqt6 = prev.pyqt6.override {
+                  #   preferWheel = true;
+                  # };
+
+                  # NOTE: this DOESN'T work atm but after a fix
+                  # to poetry2nix, it will and actually this line
+                  # won't be needed - thanks @k900:
+                  # https://github.com/nix-community/poetry2nix/pull/1257
+                  pyqt5 = prev.pyqt5.override {
+                    withWebkit = false;
+                    preferWheel = true;
+                  };
+
+                  # see PR from @k900:
+                  # https://github.com/nix-community/poetry2nix/pull/1257
+                  pyqt5-qt5 = prev.pyqt5-qt5.override {
+                    withWebkit = false;
+                    preferWheel = true;
+                  };
+
+                  # TODO: patch in an override for polars to build
+                  # from src! See the details likely needed from
+                  # the cryptography entry:
+                  # https://github.com/nix-community/poetry2nix/blob/master/overrides/default.nix#L426-L435
+                  polars = prev.polars.override {
+                    preferWheel = true;
+                  };
+                }
+              );
+            };
+        };
+
+        # output-attr that `nix-develop` scans for:
+        # https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-develop.html#flake-output-attributes
+        devShells.default = pkgs.mkShell {
+          # packages = [ poetry2nix.packages.${system}.poetry ];
+          packages = [ poetry2nix.packages.x86_64-linux.poetry ];
+          inputsFrom = [ self.packages.x86_64-linux.piker ];
+
+          # TODO: boot xonsh inside the poetry virtualenv when
+          # defined via a custom entry point?
+          # NOTE XXX: apparently DON'T do these..?
+          # shellHook = "poetry run xonsh";
+          # shellHook = "poetry shell";
+        };
+      }
+    );
+}