chore: upgrade Go toolchain to 1.25 and bump helm to v3.20.2 (#679)

* chore: upgrade Go toolchain to 1.25 and bump helm to v3.20.2

Upgrades Go from 1.24 to 1.25 in go.mod and CI workflow to fix
golangci-lint compatibility. Includes helm.sh/helm/v3 bump to v3.20.2.

Supersedes #678.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(ci): upgrade golangci-lint-action to v7 for Go 1.25 support

Action v4 installs golangci-lint v1.x which was built with Go 1.24
and refuses to lint Go 1.25 code. Action v7 uses golangci-lint v2.x
built with Go 1.25+.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: resolve golangci-lint v2 warnings

Handle Body.Close error returns and remove redundant embedded field
selector to satisfy stricter golangci-lint v2 defaults.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/build.yml

@@ -36,7 +36,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.24"
+          go-version: "1.25"
       - name: Unit tests
         run: |
           go test -v -race ./... -covermode=atomic -coverprofile=coverage.out # Run all the tests with the race detector enabled
@@ -110,13 +110,10 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.24"
+          go-version: "1.25"
       - name: golangci-lint
-        uses: golangci/golangci-lint-action@v4
+        uses: golangci/golangci-lint-action@v7
         with:
-          # version: latest
-          skip-pkg-cache: true
-          skip-build-cache: true
           args: --timeout=5m
 
       - name: Setup Node.js environment