test(module44): add tests for open-ended streams and runway top-up (closes #610)

[Ranjeet2063]

Summary

Closes #610.

This pull request provides comprehensive test coverage for open-ended streams (endTime === 0) across the Module44 runway calculator and assessment suite.

Changes Made

• Open-Ended Risk Assessment Coverage:
  • Added explicit tests for active open-ended streams asserting runwaySecs === null and riskLevel === 'healthy'.
  • Tested open-ended streams with zero rate, paused state, and cancelled state asserting proper fallback to runwaySecs === 0 and riskLevel === 'inactive'.
  • Asserted cache retrieval preserves null runway and healthy risk classification without corruption.
• Top-Up Runway Estimation Coverage:
  • Added comprehensive assertions for estimateTopUpNeeded on active open-ended streams across varied short, medium, and long target runway thresholds (10s to 1,000,000,000s) returning 0n.
  • Verified 0n return for paused, cancelled, zero-rate, and far-future timestamped open-ended streams.
• Batch Processing Parity:
  • Added mixed batch test in assessBatch verifying concurrent handling of open-ended, bounded critical, and paused streams.

Verification

• All 34/34 tests in src/tests/module44.test.ts pass cleanly.
• Full project build passes without errors (npm run build).

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