[12.x] Remove unused closure parameters in DatabaseServiceProvider

[sumaiazaman]

This PR removes unused $app parameters from closures that don't use the application container instance.

Changes:

• db.transactions singleton: Remove unused $app parameter
• ConcurrencyErrorDetectorContract singleton: Remove unused $app parameter
• LostConnectionDetectorContract singleton: Remove unused $app parameter

Benefits:

• Cleaner code that clearly shows when container access is not needed
• Eliminates unused parameter warnings in static analysis tools
• More explicit about closure dependencies
• Consistent with Laravel's coding standards

Rationale:
These closures only instantiate classes without dependencies (DatabaseTransactionsManager, ConcurrencyErrorDetector, LostConnectionDetector), so they don't need access to the application container.

Testing:

• All existing tests continue to pass
• No functional changes to service registration
• Services are still properly registered as singletons

Before:

$this->app->singleton('db.transactions', function ($app) {
    return new DatabaseTransactionsManager;
});

After:

$this->app->singleton('db.transactions', function () {
    return new DatabaseTransactionsManager;
});