fix: correct coverage source to track memu package instead of tests

[luojiyin1987]

Summary

Fixes #219

Corrected the coverage configuration to track the memu source package instead of the tests directory.

Problem

The [tool.coverage.run] source was set to ["tests"], which caused coverage to analyze test code coverage rather than the actual source code.

Solution

Changed source = ["tests"] to source = ["memu"] in pyproject.toml (line 153).

Verification

Ran pytest --cov --cov-report=term-missing and confirmed coverage now correctly reports for all src/memu/ modules.

[ankaisen]

@luojiyin1987 Thank you for your fix!