fix: send chomp timestamp as number instead of string

[Jwhiles]

Explanation

When attempting to associate an address with chomp, we would send the timestamp as a string, when the API actually expects a number. This PR changes to type, and also the call site in the upgrade controller.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

---

Note

Medium Risk
Introduces a breaking type change for AssociateAddressParams.timestamp, which can impact any callers/tests still providing a string. Runtime behavior change is small and localized to the CHOMP associate-address flow.

Overview
Fixes the CHOMP associate-address flow to use a numeric Date.now() timestamp end-to-end, updating the signed message and the payload sent to ChompApiService:associateAddress (and adjusting the associated unit test).

Updates @metamask/chomp-api-service types so AssociateAddressParams.timestamp is a number (breaking change) and records the change in both packages’ changelogs.

^{Reviewed by Cursor Bugbot for commit 91e11f7. Bugbot is set up for automated code reviews on this repo. Configure here.}