Add per-actor `setproctitle` via `devx._proctitle`

New `tractor.devx._proctitle` mod sets each
sub-actor's `argv[0]` (and kernel `comm`) to
`tractor[<aid.reprol()>]` — e.g.
`tractor[doggy@1027301b]` — so `ps`/`top`/`htop`
and `acli.pytree`/reaper tooling can identify
actors at a glance without parsing full cmdlines.

Deats,
- `set_actor_proctitle()` wraps the `setproctitle`
  pkg with `ImportError` guard; optional at runtime
  but listed in `pyproject.toml` so default installs
  benefit.
- called early in `_child._actor_child_main()` after
  `Actor` construction, before `_trio_main()` entry.
- tests in `tests/devx/test_proctitle.py`: format
  unit test, `/proc/{cmdline,comm}` integration
  test, negative detection test.

Resolves #457

(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

(cherry picked from commit d60245777e)

pyproject.toml

@@ -43,10 +43,8 @@ dependencies = [
   "tricycle>=0.4.1,<0.5",
   "wrapt>=1.16.0,<2",
   "colorlog>=6.8.2,<7",
-
   # built-in multi-actor `pdb` REPL
   "pdbp>=1.8.2,<2", # windows only (from `pdbp`)
-
   # typed IPC msging
   "msgspec>=0.20.0",
   "bidict>=0.23.1",