docs(state): correct state, migration, development and example docs against master

[allen0099]

Docs and docstring accuracy audit for OAuth state, the 0.4.0 migration guide, the development guide and the examples, checked against master. Docs and docstrings/comments only; no code change (AST-compared against master).

Corrections

docs/MIGRATING_0_4.md (+ zh-TW)

• Redis encoding: the page said any encoding emits a DeprecationWarning. In backends/redis.py (_warn_encoding), only a UTF-8 alias passed to AsyncRedisCacheBackend gets the DeprecationWarning; any other value gets only a RuntimeWarning (whose message announces the removal). A RedisConfig that sets encoding warns in load_from_config() (DeprecationWarning, plus the RuntimeWarning for non-UTF-8). The summary table row now names the RuntimeWarning too.
• Monitoring routes: the UserWarning for a missing dependencies is new in 0.3.9, not "0.3.x".

docs/STATE.md (+ zh-TW)

• The INFO-logging note applies to consume_state(); validate_state() / get_state_metadata() log a missing or expired state at DEBUG.
• InvalidStateError in the exception tree also covers a binding mismatch.

docs/DEVELOPMENT.md

• Opted-out coverage figures: a run with no live servers measures about 94.5% total and 42% for redis.py (was 92.2% / 27%).
• "Checking that a test can fail": git stash -- fastapi_cachex/ reverts changes rather than creating a mutation; the block now says to edit a function and restore with git checkout.
• Release steps: the release body starts with the notice when there is one; the GitHub release is created from release-notes.md, to which the workflow appends the installation snippet and (with a previous tag) the compare link.

Docstrings and comments

• fastapi_cachex/state/manager.py: the module/class docstrings no longer mention session state; __init__ and create_state document TypeError (float/bool TTL) and ValueError above MAX_TTL (from validate_ttl); consume_state notes that backend errors propagate (Memcached's CacheXError after repeated CAS conflicts).
• fastapi_cachex/state/exceptions.py: InvalidStateError mentions a binding mismatch.
• scripts/changelog_release.py: the module docstring mentions the notice copied to the top of the release body.
• examples/session_redis.py, examples/session_jwt.py: in 0.3.9, ClientIPDep gets the manager the middleware registered on app.state and warns when the proxy holds a different one. Only 0.4.0 resolves it through the proxy.
• examples/redis_backend.py: the lifespan creates the client, which connects lazily; it does not connect on startup.

Possible code issues (not changed here)

• fastapi_cachex/state/manager.py _decode_state (return StateData(**state_dict)): stored JSON that is valid but not an object (for example [1, 2]) raises TypeError instead of StateDataError, so validate_state() / get_state_metadata() raise instead of returning False / None.
• changelog.d/126.deprecated.md says any encoding passed to AsyncRedisCacheBackend gets a DeprecationWarning; a non-UTF-8 value gets only the RuntimeWarning.