Move the `Arbiter` class out of `runtime._runtime` into its
logical home at `discovery._registry` as `Registrar(Actor)`.
This completes the long-standing terminology migration from
"arbiter" to "registrar/registry" throughout the codebase.
Deats,
- add new `discovery/_registry.py` mod with `Registrar`
class + backward-compat `Arbiter = Registrar` alias.
- rename `Actor.is_arbiter` attr -> `.is_registrar`;
old attr now a `@property` with `DeprecationWarning`.
- `_root.py` imports `Registrar` directly for
root-actor instantiation.
- export `Registrar` + `Arbiter` from `tractor.__init__`.
- `_runtime.py` re-imports from `discovery._registry`
for backward compat.
Also,
- update all test files to use `.is_registrar`
(`test_local`, `test_rpc`, `test_spawning`,
`test_discovery`, `test_multi_program`).
- update "arbiter" -> "registrar" in comments/docstrings
across `_discovery.py`, `_server.py`, `_transport.py`,
`_testing/pytest.py`, and examples.
- drop resolved TODOs from `_runtime.py` and `_root.py`.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Gud Boi
9ec2749ab7