docs: put Sentry inside the exception handler in the documented interceptor order

[AlexeyShalaev]

Summary

The module docstring of grpc_server_kit/aio/interceptors/__init__.py gave the canonical order with AsyncSentryInterceptor (5) outside AsyncExceptionHandlerInterceptor (6). Everything else says the opposite: the AsyncSentryInterceptor docstring, GrpcServerInterceptorsProvider, the README, the quickstart, interceptors and observability guides, docs/agents.md and examples/observability_chain.py. Following the docstring, Sentry only sees the AbortError the handler produces and captures nothing.

• Swapped items 5 and 6 and added one line on why Sentry sits inside the handler.
• New unit test: reads the numbered list out of the module docstring and compares it with the chain grpc_server_providers() builds (minus DishkaAioInterceptor). The docstring and the provider drifted apart once; the test keeps them together. With master's docstring it fails at index 4 ('AsyncSentryInterceptor' != 'AsyncExceptionHandlerInterceptor').

No code change; the rest of the docs were already right. The API reference page renders this docstring, so it picks the fix up on the next docs build.

Tests

• ruff check, ruff format --check, mypy grpc_server_kit: clean.
• pytest --cov: 439 passed, 97.60% coverage.

Type of change

• Documentation update

Checklist

• Tests added or updated
• make check passes locally (ruff + mypy)
• Conventional-commit title (the changelog is generated by Release Please — do not edit it by hand)
• Documentation updated (if the public API changed), docs/agents.md included — no API change; docs/agents.md already had the right order

Related issues

Fixes #49