fix: remove nest_asyncio dependency for Python 3.12+ compatibility

[Kubudak90]

Summary

Fixes #591 - Removes the unmaintained nest_asyncio library which is incompatible with Python 3.12+ and modern uvicorn.

Problem

nest_asyncio monkey-patches asyncio.run() with a signature that doesn't support the loop_factory parameter introduced in Python 3.12. This causes failures when using modern uvicorn or other async frameworks:

Additionally, nest_asyncio is no longer maintained.

Solution

Replaced nest_asyncio with a modern, non-monkey-patching approach:

1. Added _is_event_loop_running() - Detects if we're already in an event loop
2. Updated _run_async() - Handles both sync and async contexts:
   • If in an event loop: Uses asyncio.run_coroutine_threadsafe() for safe execution
   • If not in an event loop: Uses standard asyncio.run()
3. Removed nest-asyncio from dependencies in pyproject.toml

Changes

• python/cdp/evm_local_account.py: Removed nest_asyncio, updated async handling
• python/pyproject.toml: Removed nest-asyncio dependency

Testing

The new implementation maintains backward compatibility while fixing Python 3.12+ issues. The _run_async function is used internally by EvmLocalAccount for signing operations.

Checklist

• Code follows project style guidelines
• Self-review completed
• Changes are backward compatible
• Fixes Python: Move away from nest_async (is not compatible with modern Python) and is unmaintained. #591

[cb-heimdall]

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