test: add E2E and simulation tests for pk-index compaction

[silver-ymz]

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What's changed and what's your intention?

Stack: PR 6 of 6 for iceberg pk-index compaction (← #26566)

Adds end-to-end SLT tests, simulation (madsim) failpoint tests, and integration test infrastructure for pk-index compaction.

E2E tests:

• compaction_delete_then_reinsert.slt: verifies correct position delete compaction when records are deleted and reinserted
• compaction_no_concurrent_delete.slt: verifies compaction correctness without concurrent deletes

Simulation tests:

• Rename iceberg_v3_2pc test directory → iceberg_pk_index to reflect the feature under test
• New failpoint tests: failpoint_limited_test_pk_index_compaction_* exercising the compaction lifecycle under controlled failure conditions
• cluster.rs: add DedicatedIceberg compactor mode for simulation
• main.rs: register --compactor-mode dedicated-iceberg
• Mock catalog helpers and test utilities for compaction scenarios

Misc:

• storage/compactor/src/lib.rs: add #[cfg(madsim)] export for simulated compaction result injection

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.

[silver-ymz]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• test: add E2E and simulation tests for pk-index compaction #26567 👈 (View in Graphite)
• feat: coordinate pk-index compaction via barrier checkpoint and commit #26566
• feat: wire pk-index compaction to stream task and iceberg compactor #26565
• feat: add pk-index compaction resolver and apply stream operators #26564
• refactor: extract position delete helpers and simplify pk-index writer #26563
• refactor: introduce IcebergCompactionTaskId type #26562
• main

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