feat(frontend): add source backfill progress tracking

[kwannoel]

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What's changed and what's your intention?

Tests are in the downstream PR, after we support source backfill order control.

Added support for tracking source backfill progress through a new internal table function internal_source_backfill_progress(). This function allows users to monitor the progress of source backfill operations, similar to how the existing internal_backfill_progress() function works for regular backfills.

The implementation includes:

• Added a new table function type INTERNAL_SOURCE_BACKFILL_PROGRESS in the protocol buffer
• Created a new rule TableFunctionToInternalSourceBackfillProgressRule to transform the function call into a plan that scans source backfill state tables
• Added helper functions to identify source backfill tables
• Added an end-to-end test for backfill progress monitoring

This change enables better observability into source backfill operations, which is particularly useful for debugging and monitoring large backfill jobs.

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• I have checked the Release Timeline and Currently Supported Versions to determine which release branches I need to cherry-pick this PR into.

[kwannoel]

• feat(stream): support snapshot backfill in backfill order control #22215
• feat(stream): support source backfill in backfill order control #22199
• feat(catalog): support source backfill progress in rw_fragment_backfill_progress #22218
• feat(frontend): add source backfill progress tracking #22217 👈 (View in Graphite)
• feat(frontend): support fragment level progress for snapshot backfill #22166
• feat(catalog): add fragment backfill progress view #22124
• feat(catalog): add rw_table_scan system catalog #22123
• feat(frontend): support querying internal backfill table progress #22122
• main

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