feat(core): support context manager dependency factories

[mghalix]

Summary

@contextmanager and @asynccontextmanager factories can now be used as
Wireme dependencies. Previously they resolved to an unentered context
manager object instead of the dependency, so an existing resource had to be
rewritten as a bare generator function to be injectable.

One private _normalize_factory() recognizes the two contextlib
decorators by the code object their helper closures share, and returns the
generator function they wrap. It runs wherever a factory enters Wireme:

• wired()
• override_dependency() (original and replacement)
• the bridged-adapter lookup behind override_web_dependency()

so declaration and override sites agree on one identity per dependency.
Normalizing only in wired() would register the dependency under the
wrapped generator while both override entry points still keyed on the
decorator helper, and overrides would silently do nothing.

Detection is narrow on purpose. inspect.unwrap() follows every
__wrapped__ chain, so it also strips unrelated functools.wraps
decorators, including functools.lru_cache, and silently changes their
behavior. Regression tests cover both cases.

wired() gains AbstractContextManager[R] and
AbstractAsyncContextManager[R] overloads, so a decorated factory infers
R rather than the context manager type.

Behavior is unchanged for every existing dependency form. Recorded in
ADR 0020.

Coverage

• unit: sync and async context manager dependencies, cleanup after an
  endpoint exception, override by another context manager and by a plain
  factory, functools.wraps decorator preserved, lru_cache preserved
• integration: FastAPI request lifecycle for both decorators, a context
  manager nested inside a generator closing in reverse order, and
  override_web_dependency on a bridged context manager factory
• typing: assert_type(wired(cm), str) fixtures for both decorators
• smoke: the built wheel and sdist exercise a real FastAPI request through
  a context manager dependency
• examples: context_managers.py and fastapi_context_managers.py, both
  self-checking, on stdlib sqlite3 only

Checklist

• The pull request title follows Conventional Commits; it becomes the
  default-branch commit and generated release-note entry.
• Tests cover the changed behavior.
• Documentation and examples reflect public changes.
• The appropriate release-note label is applied, or skip-changelog is
  applied for changes users do not need to see.
• just check passes locally.

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