feat: implement storeGroupValue and getGroupValue with unified locator

- API Refactoring: Extracted GroupValueLocator input type to unify parameters for storeGroupValue (mutation) and getGroupValue (query).

- Data Retrieval: Implemented getGroupValue query to allow direct retrieval of JSON values stored in host groups via Zabbix Trapper items.

- Enhanced Logic: Added ZabbixGetGroupValueRequest to fetch latest history values for group-associated items.

- Improved Verification: Updated the regression suite (REG-STORE) to include a full 'Store-Update-Retrieve' verification cycle.

- Documentation:

    - Updated docs/howtos/cookbook.md recipes to use the new locator structure and getGroupValue for verification.

    - Updated sample query files (docs/queries/) with corrected variables and verification queries.

- Tests:

    - Added unit and integration tests for getGroupValue.

    - Updated existing tests to match the refactored storeGroupValue schema.

- Verification: Verified 100% pass rate for all 16 regression steps and all unit/integration tests.

docs/howtos/maintenance.md

@@ -40,7 +40,7 @@ For running integration tests against a real Zabbix instance, it is recommended
 #### Adding New Tests
 - **Location**: Place new test files in `src/test/` with the `.test.ts` extension.
 - **Coverage**: Ensure you cover both successful operations and error scenarios.
-- **Test Specification**: Every new test must be documented in the [Test Specification](../tests.md).
+- **Test Specification**: Every new test must be documented in the [Test Specification](../testcases/tests.md).
 - **Best Practice**: If you find a bug, first create a reproduction test in `src/test/` to verify the fix.
 
 ## 🔄 Updating Dependencies