fix(BA-1976): Make AsyncEtcd an explicit async context manager

[achimnol]

resolves #xxx (BA-1976)

Now we can leverage:

• fix: Segfault/GIL state violation upon Python shutdown etcd-client-py#14
• feat: Automate tokio runtime cleanup via reference counting etcd-client-py#17

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue

[Copilot]

Pull request overview

This PR updates the etcd-client-py dependency from version 0.4.1 to 0.5.1 and refactors the AsyncEtcd wrapper to be an explicit async context manager. The changes leverage improvements in the etcd-client-py library that ensure graceful tokio runtime shutdown, eliminating the need for manual workarounds.

Changes:

• Updated etcd-client-py from 0.4.1 to 0.5.1 and testcontainers from 4.8.1 to 4.13.3
• Made AsyncEtcd and LegacyEtcdLoader explicit async context managers with aenter and aexit methods
• Refactored all AsyncEtcd usage sites to use async with context managers instead of manual close() calls

Reviewed changes

Copilot reviewed 18 out of 20 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/ai/backend/common/etcd.py	Added async context manager protocol to AsyncEtcd with aenter and aexit methods
src/ai/backend/manager/config/loader/legacy_etcd_loader.py	Added async context manager protocol to LegacyEtcdLoader
src/ai/backend/storage/server.py	Updated etcd_ctx to use async with instead of manual close()
src/ai/backend/storage/dependencies/infrastructure/etcd.py	Updated provide method to use async with pattern
src/ai/backend/manager/server.py	Refactored etcd_ctx to initialize etcd within async with
src/ai/backend/manager/dependencies/bootstrap/etcd.py	Updated provide method to use async with pattern
src/ai/backend/manager/cli/context.py	Refactored etcd_ctx, config_ctx, and redis_ctx to use async with patterns
src/ai/backend/install/context.py	Updated etcd_ctx to use async with instead of manual close()
src/ai/backend/agent/server.py	Updated etcd_ctx to use async with instead of manual close()
src/ai/backend/agent/dependencies/bootstrap/etcd.py	Updated provide method to use async with pattern
src/ai/backend/cli/main.py	Removed workaround sleep for tokio/pyo3-async-runtimes shutdown race
tests/conftest.py	Updated test fixtures to use async with pattern
tests/unit/common/conftest.py	Updated gateway_etcd fixture to use async with
tests/unit/common/test_distributed.py	Updated test to use async with for AsyncEtcd
tests/unit/common/health_checker/checkers/test_etcd.py	Updated test fixtures to use async with
tests/unit/storage-proxy/conftest.py	Changed mock_etcd to async fixture using async with
tests/unit/storage/dependencies/infrastructure/test_redis.py	Updated test fixture to use async with
requirements.txt	Updated etcd-client-py and testcontainers versions
python.lock	Updated lock file with new dependency versions
changes/5289.fix.md	Added changelog entry

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[Copilot]

The exc_type, exc_val, and exc_tb parameters should be Optional types to match Python's async context manager protocol. The correct signature should be exc_type: Optional[type[BaseException]], exc_val: Optional[BaseException], exc_tb: Optional[TracebackType]. This ensures the type hints match the protocol when aexit is called without an exception (None values).

Suggested change

	exc_type: type[BaseException],
	exc_val: BaseException,
	exc_tb: TracebackType,
	exc_type: Optional[type[BaseException]],
	exc_val: Optional[BaseException],
	exc_tb: Optional[TracebackType],

[achimnol]

Confirmed successful installation in our internal dev-test farm, which had issues without asyncio.sleep(0.1) before this PR.