Cuts CI time by reusing the shared Go build/test cache across runs.
- Replace almalinux9-gobuilder:20260606 / golang:1.25 with
gobuilder:0.1.2-alma9 on every go build/test/vet step
- Wire GOCACHEPROG via go-cache-plugin against the S3 cache bucket
- Bump kubernetes resource requests/limits for Go compile steps