v0.3.0: async client, Redis backend, HTTP server

[jolovicdev]

Summary

• AsyncClient with submit(), submit_many(), serve() mirroring sync API
• AsyncResultRef with concurrent-safe async load()
• RedisStore and AsyncRedisStore with per-fingerprint locking and O(1) blob ref-counting
• Starlette HTTP server with sync and async apps, REST API
• AsyncSQLiteStore with inline blob auto_vacuum
• AsyncLocalExecutor with asyncio-native heartbeat and locking
• cashet[redis] and cashet[server] pip extras
• submit_many extracted to _batch.py, shared by both clients
• Comprehensive Redis, async, and server test suites with auto-skip

Test plan

• Redis service container in CI, tests pass across Python 3.11/3.12/3.13
• ruff check, pyright, pytest all green

🤖 Generated with Claude Code