fix(batch): validate concurrency and rate-limit pause config

[neverm1ndthat]

Fixes #1009 and #1010

Summary

Validates InvoiceBatchProcessor configuration and makes the rate-limit backoff monotonic.

Issue #1010 - Concurrency bounds

The old code accepted non-integer, negative, zero, NaN, and Infinity values for maxConcurrent. Infinity or extremely large integers could stall the initial launch loop.

Fix:

1. Reject maxConcurrent that is not a positive integer before any dispatch
2. Cap initial launch count at Math.min(maxConcurrent, invoiceIds.length)

Issue #1009 - Rate-limit pause authority

The old code accepted negative, fractional, NaN, and Infinity pauses. A second worker with a shorter Retry-After hint could shorten the shared pause. A worker falling asleep before a longer hint arrived would dispatch immediately on wake.

Fix:

1. Validate rateLimitPauseMs is a non-negative integer
2. Validate Retry-After hints via isValidPauseMs before using them
3. Make pausedUntil monotonic: pausedUntil = Math.max(pausedUntil, nextPausedUntil)
4. Workers recheck the pause deadline after each sleep via waitForGlobalPause() loop

Testing

• All 6 existing tests in test/invoiceBatchProcessor.test.ts continue to pass
• No new files or dependencies introduced

[neverm1ndthat]

Hi @Kingsman-99! This PR addresses Issues #1009 and #1010 - validates InvoiceBatchProcessor config (maxConcurrent must be positive int, rateLimitPauseMs must be non-negative), makes the rate-limit pause deadline monotonic, and caps initial launches at invoice count. All existing tests pass. PTAL!