Preserve decimal Customer.io timestamps

[jcpsimmons]

Keeps decimal numeric timestamps unchanged during Customer.io timestamp normalization.

Testing

Verified locally under Node 22.13.1:

• TZ=UTC yarn cloud test --testPathPattern=src/destinations/customerio/__tests__/utils.test.ts ✅

• ./bin/run serve --destination=customerio -n boots successfully and exposes the Customer.io action routes ✅

• End-to-end testing using the local server was completed ✅

• Added unit tests for new functionality

• Tested end-to-end using the local server

• [If destination is already live] Tested for backward compatibility of destination. Note: New required fields are a breaking change.

• [Segmenters] Tested in the staging environment

• [If applicable for this change] Tested for regression with Hadron.

Security Review

No field definitions or credential handling were changed in this PR.

• Reviewed all field definitions for sensitive data (API keys, tokens, passwords, client secrets) and confirmed they use type password

New Destination Checklist

Not applicable.

• Extracted all action API versions to verioning-info.ts file. example

[jcpsimmons]

This draft is 1 of 3 upstream Customer.io PRs for CDP-4750.

Scope here: only decimal timestamp pass-through in convertValidTimestamp() plus a focused utility test.

Not in this PR:

• Track API batch multi-status parsing
• preset/default-subscription parity

Companion drafts:

• Parse Customer.io Track API batch multi-status responses #3657 Track API multi-status parsing
• Align Customer.io preset subscriptions with reserved events #3655 preset/default-subscription parity

This supersedes the timestamp normalization portion of the older combined draft #3654.

[jcpsimmons]

Hi @joe-ayoub-segment could I please have review on this when you get a chance? 🙏