Adapter

[MikiEEE]

Summary

This PR adds dependency-free execution adapters that let SmallOS tasks cooperate with libraries using blocking or asyncio-based runtime models.

• Adds ThreadAdapter for blocking callables and synchronous database drivers.
• Adds AsyncioAdapter backed by one persistent asyncio loop thread.
• Introduces a shared adapter_call scheduler path for future adapter types.
• Uses readiness-based completion notifications instead of scheduler polling.
• Preserves user-library exception types at the await adapter.call(...) boundary.
• Supports bounded capacity, cancellation, deterministic shutdown, and adapter diagnostics.
• Keeps database connections, transactions, pooling, retries, and library dependencies in user code.
• Adds modern generic typing so adapter results retain their callable return types.
• Keeps desktop adapter imports out of core and MicroPython-oriented import paths.
• Adds no runtime dependencies.

Examples

Standard-library-only examples demonstrate:

• Blocking callable execution alongside ordinary SmallOS tasks.
• A thread-affine sqlite3 connection using ThreadAdapter(max_workers=1).
• Persistent asyncio queues, futures, and background tasks using AsyncioAdapter.

Safety and lifecycle

• Adapters bind to one SmallOS runtime.
• max_pending rejects excess work without blocking the scheduler.
• Running Python threads cannot be forcibly cancelled.
• Asyncio cancellation is requested on the adapter loop but may be delayed by foreign code.
• Malformed adapter completions are rejected with AdapterProtocolError.
• Unexpected asyncio loop or teardown failures are exposed through shutdown_error.

Validation

• All 94 unit tests pass.
• Branch coverage passes at 65%.
• Pyright reports 0 errors and 0 warnings.
• All three adapter demos pass.
• Package, test, and demo compilation passes.
• Wheel and source distributions build successfully.
• Built artifacts include the adapters, examples, and typing contract.
• Package metadata retains zero base runtime dependencies.