Fix Iceberg streaming resume, deletion detection, and no_action handling

[tlee732]

Summary

• Separate streaming resume from SQL fields — New lastSyncedVersion field on SyncToExternalCommand keeps streaming incremental resume independent from fromVersion (Delta SQL) and fromSnapshot (Iceberg SQL). Streaming resume is now format-agnostic; format-specific routing happens at the scanner call site.
• Incremental deletion detection — Enhanced manifest set-difference in DistributedSourceScanner reads entries from both old-only and new-only manifests, computing file-level adds AND deletes. Previously only detected new files, missing deletions entirely.
• Invalidation-only commit path — When files are deleted from source but nothing new needs indexing, remove actions are now committed directly instead of being silently dropped by the empty batch loop.
• Auto-resume for one-shot syncs — Non-streaming re-syncs now read lastSyncedVersion from the companion transaction log to enable incremental fast path and correct no_action detection.

Supersedes #263 and #264. Fixes #267, #268, #270.

Test plan

export JAVA_HOME=/opt/homebrew/opt/openjdk@11

# Iceberg streaming E2E (incremental resume + FROM SNAPSHOT + invalidation-only):
mvn test-compile scalatest:test -DwildcardSuites='io.indextables.spark.sql.StreamingCompanionIcebergEndToEndTest'

# Iceberg incremental scanner (no-op, append, delete detection):
mvn test-compile scalatest:test -DwildcardSuites='io.indextables.spark.sync.DistributedSourceScannerTest'

# FROM SNAPSHOT time-travel:
mvn test-compile scalatest:test -DwildcardSuites='io.indextables.spark.sync.IcebergMiscFeaturesTest'

# SQL parsing (FROM SNAPSHOT + WITH STREAMING):
mvn test-compile scalatest:test -DwildcardSuites='io.indextables.spark.sql.SyncToExternalParsingTest'

# Delta streaming (unchanged behavior):
mvn test-compile scalatest:test -DwildcardSuites='io.indextables.spark.sql.StreamingCompanionEndToEndTest'

All tests pass (8 new tests added).

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