Ensure Logs Are Captured for Assertions and Printed During Tests

[raymondkfcheung]

This PR enhances test_log_capture, ensuring logs are captured for assertions and printed to the console during test execution.

Motivation

• Partially addresses [XCM] Observability & Debuggability #6119 and Add a logger to unit tests #6125, to improves developer tracing and debugging in XCM-related tests.
• Builds on Enhance XCM Debugging with Log Capture in Unit Tests #7594, improving log visibility while maintaining test log capture capabilities.
• While writing tests for Add EventEmitter to XCM Executor #7234, I noticed this function was missing. This PR adds it to streamline log handling in unit tests.

Changes

• Ensures logs up to TRACE level are captured (for assertions) and printed (for visibility).
• Refines documentation to clearly specify when to use each function.
• Removes ANSI escape codes from captured logs to ensure clean, readable assertions.

When to Use?

Usage	Captures Logs?	Prints Logs?	Example
init_log_capture(LevelFilter::INFO, false)	✅ Yes	❌ No	Capture logs for assertions without printing.
init_log_capture(LevelFilter::TRACE, true)	✅ Yes	✅ Yes	Capture logs and print them in test output.
sp_tracing::init_for_tests()	❌ No	✅ Yes	Print logs to the console without capturing.

[raymondkfcheung]

/cmd prdoc --audience runtime_dev --bump minor

[raymondkfcheung]

/cmd fmt

[raymondkfcheung]

/cmd fmt

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs.
Job name: build-test-collators
Logs: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/8301234

[raymondkfcheung]

/cmd fmt

[raymondkfcheung]

/cmd fmt

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/13675331552
Failed job name: test-linux-stable