v0.10.1 — async, smart routing, observability, plugins + full-project review

The 0.10 line adds four features and a full-project review pass.

New (0.10.0)

• Async — from freellmpool import AsyncPool: await pool.aask/achat over httpx.AsyncClient, same failover/cooldown/quota/metrics/cache as the sync Pool.
• Metrics-aware routing + freellmpool benchmark — per-provider EWMA latency + success rate. Default fair routing sinks failing providers; FREELLMPOOL_ROUTING=fast prefers lowest latency.
• Observability — on_event= hook (attempt/success/error/cooldown/exhausted) on both pools; FREELLMPOOL_LOG enables logging in the CLI/proxy.
• Plugins — register_provider() / register_adapter() + a freellmpool.providers entry-point group.

Hardened (0.10.1)

A full-project review (Codex full pass + an independent manual pass + a Codex re-verify, reconciled to consensus) fixed:

• proxy: socket read timeout + daemon worker threads; streaming+tools now carries tool_calls (with per-call index); mid-stream errors close the SSE cleanly; content:null no longer becomes "None"; embeddings honor a pinned provider/model; Anthropic /v1/messages returns Anthropic-shaped errors.
• quota: cross-process safe (POSIX flock + reload-merge).
• MCP: JSON-RPC parse/invalid-request/batch per spec.
• cache: sqlite connections explicitly closed (were leaking fds).

Also renamed the base exception BuffetError → FreeLLMPoolError (deprecated alias kept).

153 tests, ruff clean. Full notes in CHANGELOG.md.