Summary

Fixes #1115.

A response close interrupted by cancellation used to leave both byte-stream wrappers marked closed before their cleanup completed. Any later close then returned immediately, leaving the pool request and its HTTP/1.1 connection counted as active. This is the connection leak reported in encode/httpx#3782.

The wrappers now serialize close calls and set _closed only after the inner close and pool bookkeeping succeed. An interrupted close therefore remains retryable. The generated synchronous implementations are kept in step with the async sources, as required by the repository.

The regression test interrupts the network close with CancelledError, confirms the pool is still occupied, retries response.aclose(), and verifies that the request and connection are removed. The test fails against master with one active request and connection.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• Documentation is unaffected because this restores the existing close contract.

Validation:

• Relevant async and sync HTTP/1.1, connection-pool, and cancellation tests: 99 passed, 6 existing xfails xpassed
• Repository-pinned Ruff formatting and lint checks
• Mypy on the four changed implementation files
• scripts/unasync.py --check