GitLab Credits usage order: included credits before evaluation credits

This issue is the public record for the GitLab 19.4 release note. Implementation was tracked in internal issues.

GitLab Credits are now consumed in a new order when a subscription has temporary evaluation credits. Each user's included monthly credits are used first, and the shared pool of temporary evaluation credits is used only after a user has consumed their own included amount. Previously all usage drew from the evaluation pool first, so included credits sat unused until the end of the month.

The Monthly Commitment Pool, One-Time Charge credits, and On-Demand credits are consumed in the same order as before, so billing is unaffected.

Shipped in GitLab 19.4. Documentation: https://docs.gitlab.com/subscriptions/gitlab_credits/#usage-order