Enhanced the demo test to cover more go/build functionality:
- build.Import (existing)
- build.ImportDir (new)
- build.IsLocalImport (new)
- build.Default context verification (existing, improved)
This ensures the go/build patches work correctly across different
public functions, not just Import.
Also ran go fmt to fix formatting issues reported by CI.
🤖 Generated with [codeagent](https://github.com/qbox/codeagent)
Co-authored-by: luoliwoshang <luoliwoshang@users.noreply.github.com>
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