Refactor Test Suite: Modularize and Expand Coverage

[haroonwaves]

Improve the maintainability and reliability of the @ramifyjs/core test suite by splitting tests into module-specific files and closing gaps in coverage.

Key Objectives:

Module-wise Split: Decouple the monolithic test file into dedicated files for core modules

• collection.test.ts: CRUD, bulk operations, and index management.
• query.test.ts: Fluent API filtering, sorting, and results processing.
• ramify.test.ts: Store initialization and collection management.
• observer.test.ts: Subscription and notification logic.

Comprehensive Coverage: Ensure all edge cases are covered, specifically:

• Validation errors (e.g., non-primitive primary keys).
• Newer features like .modify() and the $allOf operator.
• Bulk operation side effects and observer notifications.