refactor: emit integration diagnostics via STDERR

[rbcorrales]

Summary

Replaces the two raw error_log() calls in tests/integration/DatabaseIntegrationTest.php with fwrite( STDERR, ... ).

Background

Closes out the long-running error_log() -> Logger cleanup. Production includes/ already routes through WPVDB\Logger (the only sanctioned raw error_log() is the centralized, phpcs-ignored sink at class-wpvdb-logger.php:174). The last raw calls were these two integration-test diagnostics.

fwrite( STDERR, ... ) is the right fit here rather than Logger:

• They are deliberate test diagnostics (vector-support and insert/query timing) that should always print during a test run. Logger::debug() is gated behind wpvdb_should_log_to_error_log() and would silence them.
• fwrite( STDERR, ... ) is the PHPUnit-idiomatic way to emit a diagnostic and avoids the WordPress.PHP.DevelopmentFunctions.error_log_error_log smell.

After this, no raw error_log() calls remain anywhere except the sanctioned sink.

Testing

php -l clean. Behavior preserved (diagnostics still print, now to STDERR). Note: this test file is integration-only (self-skips without a real DB) and is outside the phpcs scan surface, so this is a focused 3-line change.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR refactors integration-test diagnostics by replacing raw error_log() calls with fwrite( STDERR, ... ), aligning the test suite with the codebase’s logging cleanup while preserving always-on diagnostic output during PHPUnit runs.

Changes:

• Replace two error_log() diagnostics with fwrite( STDERR, ... ) in the integration test suite.
• Add/adjust diagnostic comment text and ensure diagnostics include trailing newlines.

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