Standardizes on the estate gobuilder image for every step invoking
the Go toolchain and wires in the shared S3-backed GOCACHEPROG.
- Replace golang:1.25 and almalinux9-gobuilder:20260606 with
gobuilder:0.1.2-alma9 in build/test/pre-commit/release(build)
- Add GOCACHE_* env + AWS creds from org secrets to those steps
- Bump their k8s resource requests/limits for compile+cache overhead