test(golang_router): add cleanup and cross-day rolling coverage for logger

[mouxinqq]

Motivation

• Ensure StartLogCleanup behavior is covered for file output, ensuring expired archived logs are removed, recent/today files are preserved, and the cleanup goroutine stops on context cancellation.
• Validate rotating writer day-rollover behavior including the grace-period routing of late previous-day log lines and symlink update semantics.

Description

• Added unit tests in fastdeploy/golang_router/pkg/logger/logger_test.go to exercise StartLogCleanup with a controlled nowFunc, temporary log directory, and context cancellation.
• Added an integration-style test for rotatingWriter that simulates a cross-day transition and verifies that late previous-day lines are written to the previous-day file and that router.log symlink points to the new day file.
• Introduced a waitForCondition helper and adjusted imports to support time control and temporary directories used by the tests.

Testing

• Ran cd fastdeploy/golang_router && go test ./pkg/logger and the package tests passed (ok).
• The new tests exercised TestStartLogCleanup and TestRotatingWriterCrossDayGracePeriodIntegration as part of the package test run and succeeded.

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Codex Task