fix(multiscan): preserve scan outcome and record receipt when checkout cleanup fails

[Ultron09]

Summary

Preserve multiscan attempt outcomes and ensure attempt receipts are durably recorded in results.jsonl when checkout directory removal encounters secondary filesystem errors (such as EACCES, EPERM, or EBUSY).

Fixes #211.

Changes

• In sdk/typescript/src/multiscan.ts, decouple the checkout removal cleanup step from the primary scan outcome capture and receipt appending.
• Treat checkout removal as best-effort cleanup: capture cleanup exceptions without aborting the worker, record the authentic scan attempt status (completed, completed_with_incomplete_coverage, or failed) in the ledger receipt, and emit a non-fatal warning on progress notifications.
• Ensure that if an abort signal is triggered, checkout removal is attempted before rethrowing.
• In sdk/typescript/tests-ts/multiscan.test.ts, add regression tests verifying:
  1. A scan failure followed by a checkout cleanup error preserves the original scan failure in the ledger receipt and progress notifications.
  2. A scan success followed by a checkout cleanup error preserves the completed status in the ledger receipt, counts the completion, and does not crash the campaign.

Testing

• bun test ./tests-ts/multiscan.test.ts (53 pass, 2 skip, 0 fail)
• pnpm --dir sdk/typescript run types (passed with 0 errors)
• pnpm --dir sdk/typescript run format (passed with all files formatted)
• python .github/scripts/check_plugin_source_compatibility.py (passed)

Risk and rollout

Low. This change makes multiscan worker cleanup resilient without modifying the scan execution or ledger format contract.

Public disclosure review

• No customer, partner, prospect, or user identities, data, or identifying details are included.
• No credentials, personal data, private source, scan findings, or nonpublic links or tickets are included.
• I reviewed the branch name, title, description, commits, changes, comments, logs, screenshots, attachments, and links for public disclosure.