fix(scanner): optimize removal of immutable scanners with bulk deletion

[vishalmore90]

Comprehensive Summary of your change

This PR resolves an N+1 query performance issue in the RemoveImmutableScanners initialization step.

Previously, when clearing out old immutable scanners, RemoveImmutableScanners retrieved all relevant scanner registrations from the database and executed an individual DELETE query for each scanner in a loop. For setups with multiple scanners being cycled or cleared out, this generated unnecessary DB traffic and latency.

This PR implements a bulk-deletion method (DeleteRegistrations) in the scanner data access object (dao/scanner/registration.go), wires it through the scanner Manager interface as DeleteBy, and updates RemoveImmutableScanners in init.go to use this new method. It completely replaces the N+1 DELETE loop with a single bulk query, resolving the documented TODO. Unit tests and mocks have been appropriately updated and verified.

Issue being fixed

Fixes #24022

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