…ignal handler

Replace module setattr + Python string exec with:
- OnceLock<Py<PyAny>> static for the exception class
- Rust #[pyfunction] signal handler

Eliminates a setattr on the coglet module (needed for upcoming
module write protection) and removes Python-as-string.

…g target

audit.rs:
- Replace 60-line Python string with Rust #[pyfunction] audit hook
- Add AtomicBool re-entrancy guard (replaces threading.Timer hack)
- Add Mutex to serialize stream replacement across threads
- Demote helper functions from #[pyfunction] to pub(crate)
- Rename TeeWriter -> _TeeWriter (private pyclass)

worker_tracing_layer.rs:
- Add coglet::worker_local target filter (excluded from IPC,
  always written to worker stderr fd 101)
- Used by audit.rs for poisoned-lock diagnostics that must not
  traverse the log routing infrastructure

Make the log writer class private in the Python namespace via
pyclass(name = "_SlotLogWriter"). Rust type name unchanged.

…edictor

Move _collect_async_gen and _ctx_wrapper Python async helper functions
into OnceLock statics so they are defined once and reused across calls.
Fix Py<PyAny>::call1() call sites to pass py token as first argument.

…tr__

- Remove standalone active() #[pyfunction], expose via __getattr__ as
  property-like attribute (no parens needed)
- Add __getattr__ for 'active' and '__build__' attribute access
- Add __dir__ returning only public API: __version__, __build__, active, serve
- Add __setattr__ to block writes to module (registered LAST in init)
- Use PEP 440 version from COGLET_PEP440_VERSION env var
- Store BuildInfo as _build_info, exposed as __build__ via __getattr__

- coglet.server: frozen Server pyclass with .active property, .serve(),
  ._run_worker(), ._is_cancelable()
- coglet._sdk: submodule for Python runtime integration classes
  (_SlotLogWriter, _TeeWriter)
- Root module is plain: __version__, __build__, server, _sdk
- No PEP 562 machinery needed — static attrs in dict, dynamic .active
  is a #[getter] on frozen pyclass
- Update all callsites: http.py, orchestrator.rs, tests, docs

…__.py

- coglet/__init__.py: explicit re-exports with __all__ control
- coglet/py.typed: marker for type stub distribution
- pyproject.toml: module-name = coglet._impl for mixed layout
- lib.rs: #[pyo3(name = "_impl")] + __all__ for import control
- .gitignore: add *.so, *.pyd to prevent committing build artifacts
- Maturin now builds as mixed python/rust project, no auto-generated wrapper

- Remove stale root coglet.pyi, replace with coglet/__init__.pyi (mypy
  stubgen) and coglet/_sdk/__init__.pyi (pyo3-stub-gen)
- pyproject.toml: add python-source = '.' for pyo3-stub-gen mixed layout
- mise.toml: update generate:stubs to run pyo3-stub-gen then mypy stubgen
- mise.toml: rewrite stub:check to use git diff on all .pyi files
- mise.toml: update stub:typecheck path

Tests for: PEP 440 version, BuildInfo fields/frozen/repr,
server.active property, server frozen protection, _sdk submodule
contents, __all__ excludes internals. 17 new tests, all passing.