fix: release stream reader locks on normal completion, skip unread clone (#382)

teeStream and createAnthropicTerminalRecoveryStream only released their
upstream reader's lock on the cancel/error teardown paths, never on
normal done-completion — the 96%+ traffic case. Both wrap every native
Anthropic-Messages SSE response and every proxied response body.

OpenAICompatibleProvider.extractUsageInfo cloned the response before
checking content-type, then returned null unread for SSE bodies,
leaving that clone's tee branch open on every OpenAI-compatible
streaming response. The clone now only happens on the JSON branch that
actually consumes it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>