Add checkpoint resume coverage for indexer

[kitWarse]

Summary

• Added deterministic start ledger resolution for the S03 indexer so a stored checkpoint can control the configured start block.
• Added Bun tests that simulate a stored checkpoint, verify resume from that ledger, and verify fallback to the configured genesis ledger when no checkpoint exists.

Issue

• Closes Indexer: cursor/checkpoint persistence #337

Changes

• Introduced
  esolveIndexerStartLedger in �pps/s03-indexer/project.ts.
• Supports checkpoint values from lastProcessedLedger, lastProcessedHeight, ledger, or height fields.
• Keeps the existing INDEXER_START_LEDGER fallback behavior when no checkpoint path is provided or the checkpoint is missing.
• Added focused tests in �pps/s03-indexer/tests/start-ledger.test.ts.

Validation

• Attempted: �un run --cwd apps/s03-indexer test
• Result: blocked locally because subql was not available before dependencies were installed.
• Attempted: �un install
• Result: command timed out in the local environment before validation could be rerun.

Notes

• No lockfile or dependency changes were committed.

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