fix(go): avoid false build errors from download logs

[em0t]

Summary

• tighten rtk go build error detection so dependency download/progress lines are not treated as compiler failures
• keep real compiler errors such as file.go:line:col diagnostics and explicit toolchain error lines
• add regression coverage for package names containing errors, xerrors, and multierror

Minimal Case

Raw

go: downloading github.com/pkg/errors v0.9.1
go: downloading golang.org/x/xerrors v0.0.0-20231012003039-104605ab7028

Previous RTK

Go build: 2 errors
  go: downloading github.com/pkg/errors v0.9.1
  go: downloading golang.org/x/xerrors v0.0.0-20231012003039-104605ab7028

This PR

Go build: Success

Testing

• cargo fmt --all
• cargo clippy --all-targets
• cargo test --all

Notes

• cargo clippy --all-targets still reports pre-existing warnings outside this change set

[CLAassistant]

All committers have signed the CLA.

[em0t]

Could a maintainer please approve and run workflows so CI can start for review?

[aeppling]

The old broad match caught four patterns:

• contains("error")
• contains(".go:")
• contains("undefined")
• contains("cannot")

The new is_go_build_error_line() catches:

• contains(".go:") ✓
• go: build failed, go: error, error: ✓
• But drops undefined and cannot as standalone keywords

What this misses: Go compiler errors that surface without a file.go:line:col prefix, e.g.: undefined: missingFunc cannot find package "foo/bar"

This is debatable but i think those are important if go compiler use to tell about missing import or not defined function/etc

[em0t]

Thanks @aeppling, good catch. I pushed an update that keeps the download-line false-positive fix but restores non-file build errors, including undefined: ..., cannot find package ..., import cycles, build constraint failures, and go.mod/go.work parse errors. I also added regression tests for these cases.

[em0t]

I pushed a small follow-up on top of this: the test fixture now uses only public package paths, and go build now also preserves go.mod file not found ..., no Go files in ..., and broken go.work module-loading errors.

[aeppling]

thanks for all quality filters contributions