Fix intrange and G101 linting issues

- Convert for loops to use Go 1.22+ integer ranges in generate.go and helpers.go
- Disable G101 false positives for test vectors and environment variable names
- Add file-level gosec disable for bip85_test.go containing BIP85 test vectors
- Add targeted nolint comments for legitimate test data and constants

internal/secret/helpers.go

@@ -17,7 +17,7 @@ func generateRandomString(length int, charset string) (string, error) {
 	result := make([]byte, length)
 	charsetLen := big.NewInt(int64(len(charset)))
 
-	for i := 0; i < length; i++ {
+	for i := range length {
 		randomIndex, err := rand.Int(rand.Reader, charsetLen)
 		if err != nil {
 			return "", fmt.Errorf("failed to generate random number: %w", err)