fix(go): preserve test and vet diagnostics

[jsiu93]

Closes #2281.

Summary

• Route rtk go test and rtk go vet through exit-aware filtering so non-zero Go failures cannot be summarized as empty results.
• Preserve real Go diagnostics such as undefined, cannot, and import cycle from raw output and go test -json output events.
• Share Go diagnostic formatting across build/test/vet and strip ANSI before matching.

Test plan

• cargo fmt --all -- --check
• cargo clippy --all-targets
• cargo test --all --quiet
• Manual repro: rtk go test ./... and rtk go vet ./... in a temporary Go project with undefined: missingSymbol