fix(tx): correct _tx_loop to pop _TxItem and send frames contiguously

[kstaniek]

Summary

• pop _TxItem (not raw bytes) and check item is None
• avoid variable shadowing; use frame_bytes in send loop
• on writer=None: requeue whole item, clear _connected, yield
• on write error: requeue remaining frames as one atomic item
• preserves non-interleaving batches and prevents tight re-loops

What’s changed

• Feature
• Bug fix
• Documentation
• Maintenance / Refactor
• Tests

Checklist

• Tests added/updated
• Docs updated (README/Examples/Docstrings)
• ruff check and ruff format pass
• mypy caneth passes
• CI green

[Copilot]

Pull Request Overview

This PR refactors the transmission loop in WaveShareCANClient to properly handle atomic frame batches and fix several issues with frame ordering and error recovery. The changes introduce a new _TxItem data structure to group frames atomically and ensure they are sent contiguously without interleaving.

Key changes:

• Introduces _TxItem structure to encapsulate atomic frame groups with metadata
• Refactors _tx_loop to pop entire items and send all frames within an item back-to-back
• Adds proper error handling that re-queues remaining frames atomically on write failures
• Implements atomic context manager for creating non-interleaved frame sequences

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
caneth/client.py	Core refactoring of transmission system with new _TxItem structure, updated TX loop logic, and atomic batching functionality
tests/test_atomic_context.py	Comprehensive test coverage for atomic frame transmission and mid-batch disconnect scenarios

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[Copilot]

The variable name frame_bytes shadows the outer scope variable mentioned in the PR description. Consider using a more descriptive name like frame_data or encoded_frame to avoid confusion and improve code clarity.

Suggested change

	for idx, frame_bytes in enumerate(item.frames):
	writer.write(frame_bytes)
	for idx, frame_data in enumerate(item.frames):
	writer.write(frame_data)

[Copilot]

When re-queuing remaining frames, the code always sets atomic=True regardless of the original item's atomic flag. This could change the behavior for non-atomic items. Consider preserving the original atomic value: _TxItem(frames=remaining, atomic=item.atomic, can_id=item.can_id).