ci: enable govet for test files in golangci-lint

[t-kikuc]

What this PR does

Remove run.tests: false from .golangci.yml and replace with per-linter exclusion rules, so that govet runs on test files while other linters remain excluded. Fix existing sync.Map value copy violation detected by the copylocks analyzer.

Background

.golangci.yml had run.tests: false, which excluded all test files from all linters including govet. govet has very low false-positive rates and catches real bugs — the copylocks analyzer, for example, has existed since at least Go 1.21 but its violations in test files were invisible in CI.

Other linters (errcheck, goheader, lll, etc.) can be noisy on test files, so enabling tests: true globally is not ideal. golangci-lint v2 supports per-linter exclusion via linters.exclusions.rules, which allows enabling govet for tests while keeping other linters excluded.

Verification commands

# Confirm govet detects test file issues (before the test fix)
golangci-lint run --timeout 3m0s ./pkg/api/api/...
# → 5 copylocks violations in save_api_key_last_used_at_test.go

# Confirm 0 issues after the fix
golangci-lint run --timeout 3m0s ./cmd/... ./evaluation/go/... ./pkg/... ./hack/... ./test/...
# → 0 issues

# Confirm no other govet violations exist in test files
go vet ./cmd/... ./pkg/... ./evaluation/go/...
# → 0 errors

Points

• The copylocks issue in save_api_key_last_used_at_test.go predates this PR — it was never detected because test files were excluded from linting
• The test struct fields existingCache sync.Map / expectedCache sync.Map are replaced with setupCache func(*sync.Map) / expectedCache map[string]apikeyLastUsedAt to avoid value copies of sync.Map

[Copilot]

Pull request overview

Enables govet checks for Go test files while suppressing noisier linters.

Changes:

• Replaces the global test exclusion with per-linter exclusions.
• Refactors cache tests to avoid copying sync.Map.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.golangci.yml	Enables govet for tests while excluding other linters.
pkg/api/api/save_api_key_last_used_at_test.go	Avoids sync.Map value copies in test cases.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.