[core] Make DataInstance extend AccessibleResource

[arnav-makkar]

Brief summary of changes

1. Updated the DataInstance contract to extend both \JsonSerializable and \LORIS\StudyEntities\AccessibleResource, making isAccessibleBy(\User): bool mandatory for all implementers.
2. Simplified src/Data/Filters/AccessibleResourceFilter.php by removing the runtime instanceof AccessibleResource guard and calling isAccessibleBy() directly.
3. Added src/StudyEntities/DataInstanceAccess.php to centralize common center/project access checks (including getter variants and scalar ID normalization with fail-closed behavior).
4. Added isAccessibleBy() implementations for all previously missing DataInstance classes, using shared helper logic for standard cases and explicit custom logic for exceptions (e.g., MRI violations, protocol-check violations, DICOM no-session rows, permission-gated DTOs).
5. Added coverage with new unit tests for:
   i. contract enforcement (DataInstanceContractTest)
   ii. helper behavior (DataInstanceAccessTest)
   iii. custom exception behavior (DataInstanceBehaviorTest)

Testing instructions (if applicable)

1. Run:
   docker compose run -T --rm unit-tests vendor/bin/phpunit --configuration test/phpunit.xml test/unittests/DataInstanceContractTest.php test/unittests/DataInstanceAccessTest.php test/unittests/DataInstanceBehaviorTest.php
2. Result: targeted Docker unit tests for contract + helper + exception-path behavior passed: OK (16 tests, 139 assertions)

Link(s) to related issue(s)

• Resolves DataInstance should extend AccessibleResource #9511