[Feature] Add unit tests for StartLogCatMonitor command

[ConnorQi01]

Summary

StartLogCatMonitor has no dedicated unit tests. The command covers three meaningful code paths: no device found (shows error message), device found (stops any previous monitor and starts a new one), and LogCat start failure (logs a warning). Its counterpart StopLogCatMonitor already has comprehensive tests; adding tests here completes the LogCat monitor lifecycle coverage.

Why this is useful

A regression in target selection, monitor replacement, or error propagation would silently break the Android LogCat workflow. The current test suite guards StopLogCatMonitor but leaves the start path untested.

Suggested scope

• Add test/extension/commands/startLogCatMonitor.test.ts using the proxyquire + sinon pattern from stopLogCatMonitor.test.ts.
• Stub AndroidTargetManager, LogCatMonitorManager, LogCatMonitor, SettingsHelper, TipNotificationService, OutputChannelLogger, and vscode.window.showErrorMessage.
• Test: selectAndPrepareTarget returns null → showErrorMessage called, monitor not started.
• Test: selectAndPrepareTarget returns a target → delMonitor called for previous, new monitor created and start() invoked.
• Test: logCatMonitor.start() rejects → warning logged, no error thrown from baseFn.

Evidence

• src/extension/commands/startLogCatMonitor.ts — command with three distinct code paths, no matching test file.
• test/extension/commands/stopLogCatMonitor.test.ts — established pattern for LogCat monitor command tests.
• Recent test-coverage work: StopPackager (Add StopPackager command unit tests #2790), RestartPackager (Add RestartPackager command unit tests #2795), StopLogCatMonitor cancel tests (Fix StopLogCatMonitor cancellation #2777).

Validation

• Run npm run build.
• Run npm test and confirm the new suite passes.
• startLogCatMonitor scenarios: no-device, device-found, start-error.