Use golangci-lint fmt to format code (#163)

Use `golangci-lint fmt` to format code, upgrading `.golangci.yml` to v2 and mirroring the linter configuration used by https://github.com/go-gitea/gitea. `gci` now handles import ordering into standard, project-local, blank, and default groups.

Mirrors https://github.com/go-gitea/gitea/pull/37194.

Changes:
- Upgrade `.golangci.yml` to v2 format with the same linter set as gitea (minus `prealloc`, `unparam`, `testifylint`, `nilnil` which produced too many pre-existing issues)
- Add path-based exclusions (`bodyclose`, `gosec` in tests; `gosec:G115`/`G117` globally)
- Run lint via `make lint-go` in CI instead of `golangci/golangci-lint-action`, matching the pattern used by other Gitea repos
- Apply safe auto-fixes (`modernize`, `perfsprint`, `usetesting`, etc.)
- Add explanations to existing `//nolint` directives
- Remove dead code (unused `newRemoteReusableWorkflow` and `networkName`), duplicate imports, and shadowed `max` builtins
- Replace deprecated `docker/distribution/reference` with `distribution/reference`
- Fix `Deprecated:` comment casing and simplify nil/len checks

---
This PR was written with the help of Claude Opus 4.7

Reviewed-on: https://gitea.com/gitea/act/pulls/163
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

pkg/runner/command.go

@@ -29,7 +29,7 @@ func tryParseRawActionCommand(line string) (command string, kvPairs map[string]s
 		arg = m[4]
 		ok = true
 	}
-	return
+	return command, kvPairs, arg, ok
 }
 
 func (rc *RunContext) commandHandler(ctx context.Context) common.LineHandler {
@@ -135,10 +135,10 @@ func (rc *RunContext) addPath(ctx context.Context, arg string) {
 	rc.ExtraPath = extraPath
 }
 
-func parseKeyValuePairs(kvPairs string, separator string) map[string]string {
+func parseKeyValuePairs(kvPairs, separator string) map[string]string {
 	rtn := make(map[string]string)
-	kvPairList := strings.Split(kvPairs, separator)
-	for _, kvPair := range kvPairList {
+	kvPairList := strings.SplitSeq(kvPairs, separator)
+	for kvPair := range kvPairList {
 		kv := strings.Split(kvPair, "=")
 		if len(kv) == 2 {
 			rtn[kv[0]] = kv[1]