fix: update Go version to 1.25.0 and remove toolchain directive

[KoheiMatsuno99]

upgrade go1.25
migrate golangci-lint v2

[mfridman]

Thanks! Been meaning to do this for a while.

[KoheiMatsuno99]

@mfridman

I recently migrated from golangci-lint v1 to v2 (along with Go 1.25).

During the upgrade, the revive linter's var-naming rule started failing specifically in the utils package—an error that did not occur in v1.

To unblock the migration, I temporarily disabled the var-naming rule.

❓ Question on Best Practice

Which approach do you prefer for this project?

1. Keep var-naming disabled as I did.
2. Re-enable var-naming and rename the utils package to comply with the linter.

Thank you!

[KoheiMatsuno99]

On a related note, since we are now on golangci-lint v2, I would also like to suggest adding the modernize linter.

modernize is officially provided by Go and helps to simplify code.

Would you be open to incorporating modernize into our configuration?

https://pkg.go.dev/golang.org/x/tools/gopls/internal/analysis/modernize

[mfridman]

100% should add modernize. That one is great.

utils isn't a great name, esp in bigger projects. But I'd argue it's fine for a small project like this, esp since it's internal anyways.

If you think of a better name sure, prob less interesting linter tbh.