[PR1 - refactor] Introduce branching and support for spark.wap.branch

[cbb330]

Summary

This PR extracts snapshot handling logic from OpenHouseInternalTableOperations into a dedicated SnapshotDiffApplier class. The refactoring improves code organization and maintainability while preserving all existing behavior.

Changes

• [ ] Client-facing API Changes
• [ ] Internal API Changes
• [ ] Bug Fixes
• [ ] New Features
• [ ] Performance Improvements
• [ ] Code Style
• [x] Refactoring
• [ ] Documentation
• [ ] Tests

Refactoring:

• Created new SnapshotDiffApplier service class responsible for applying snapshot changes to Iceberg table metadata
• Migrated snapshot logic from OpenHouseInternalTableOperations to SnapshotDiffApplier
• Migrated validation logic from SnapshotInspector.validateSnapshotsUpdate()
• Implemented state object pattern (SnapshotDiff) that computes and caches all snapshot analysis upfront
• Clear flow: parse input → compute diff → validate → apply → record metrics

Snapshot categorization:

• Staged (WAP) snapshots: Contain STAGED_WAP_ID_PROP in summary, added without branch reference
• Cherry-picked snapshots: Existing snapshots referenced as SOURCE_SNAPSHOT_ID_PROP by another snapshot, or WAP snapshots transitioning from staged to published
• Regular snapshots: All new snapshots that are not staged WAP snapshots
• Only EXISTING snapshots are considered as cherry-picked sources

Validation:

• Prevents deleting the current snapshot without providing replacement snapshots
• Validates only MAIN branch is supported (existing OpenHouse behavior)

Testing Done

• [ ] Manually Tested on local docker setup. Please include commands ran, and their output.
• [ ] Added new tests for the changes made.
• [ ] Updated existing tests to reflect the changes made.
• [x] No tests added or updated. Please explain why. If unsure, please feel free to ask for help.
• [ ] Some other form of testing like staging or soak time in production. Please explain.

This is a pure refactoring that extracts existing logic into a new class without changing behavior. All existing tests should continue to pass as-is since the functionality remains identical. The extracted logic maintains the same validation rules, snapshot categorization, and metrics recording as before.

Additional Information

• [ ] Breaking Changes
• [ ] Deprecations
• [ ] Large PR broken into smaller PRs, and PR plan linked in the description.