Optimize CI caches (#37387)

Cache includes go, lint and unittests. Integration tests with their
standalone binaries are uncacheable with their current architecture.

Every Go job uses a new composite action (`.github/actions/go-cache`)
that restores and saves the Go module cache, a shared build cache, and
the golangci-lint cache. A `cache-seeder` workflow runs on `push: main`
to pre-populate those slots; PRs read them via GitHub's default-branch
fallback, so the common case is warm from the first commit.

Also dropped `-coverprofile` from `test-unit` (it silently disabled Go's
test result cache), and `-race` from `test-pgsql` and `test-mysql` (kept
on `test-unit` and `test-sqlite`).

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: Nicolas <bircni@icloud.com>

.github/workflows/pull-e2e-tests.yml

@@ -25,6 +25,11 @@ jobs:
         with:
           go-version-file: go.mod
           check-latest: true
+          cache: false
+      - uses: ./.github/actions/go-cache
+        with:
+          cache-name: e2e
+          build-cache: "false"
       - uses: pnpm/action-setup@v5
       - uses: actions/setup-node@v6
         with: