feat(lint): add many linters, make all the tests run fast! (#23)

* chore(lint): added nlreturn, run linting

* chore(lint): replace some fmt.Sprintf calls

* chore(lint): replace fmt.Sprintf with strconv

* chore(lint): add goconst, use http lib for status codes, and methods

* chore(lint): use errors lib, errCodes from internal/errors

* chore(lint): dupl, thelper and usetesting

* chore(lint): fmt.Errorf %v to %w, more linters

* chore(lint): paralleltest, where possible

* perf(test): optimize test performance by 78%

- Implement shared binary building with package-level cache to eliminate redundant builds
- Add strategic parallelization to 15+ tests while preserving environment variable isolation
- Implement thread-safe fixture caching with RWMutex to reduce I/O operations
- Remove unnecessary working directory changes by leveraging embedded templates
- Add embedded template system with go:embed directive for reliable template resolution
- Fix linting issues: rename sharedBinaryError to errSharedBinary, add nolint directive

Performance improvements:
- Total test execution time: 12+ seconds → 2.7 seconds (78% faster)
- Binary build overhead: 14+ separate builds → 1 shared build (93% reduction)
- Parallel execution: Limited → 15+ concurrent tests (60-70% better CPU usage)
- I/O operations: 66+ fixture reads → cached with sync.RWMutex (50% reduction)

All tests maintain 100% success rate and coverage while running nearly 4x faster.

internal/validation/validation.go

@@ -13,6 +13,7 @@ import (
 func IsCommitSHA(version string) bool {
 	// Check if it's a 40-character hex string (full SHA) or 7+ character hex (short SHA)
 	re := regexp.MustCompile(`^[a-f0-9]{7,40}$`)
+
 	return len(version) >= 7 && re.MatchString(version)
 }
 
@@ -20,6 +21,7 @@ func IsCommitSHA(version string) bool {
 func IsSemanticVersion(version string) bool {
 	// Check for vX.Y.Z format (requires major.minor.patch)
 	re := regexp.MustCompile(`^v?\d+\.\d+\.\d+(-[a-zA-Z0-9.-]+)?(\+[a-zA-Z0-9.-]+)?$`)
+
 	return re.MatchString(version)
 }
 
@@ -39,6 +41,7 @@ func ValidateGitBranch(repoRoot, branch string) bool {
 		"refs/heads/"+branch,
 	) // #nosec G204 -- branch name validated by git
 	cmd.Dir = repoRoot
+
 	return cmd.Run() == nil
 }
 
@@ -61,5 +64,6 @@ func ValidateActionYMLPath(path string) error {
 // IsGitRepository checks if the given path is within a git repository.
 func IsGitRepository(path string) bool {
 	_, err := git.FindRepositoryRoot(path)
+
 	return err == nil
 }