fix(catalog,flow): address clippy and golangci-lint warnings

- Rust: remove needless Ok(x?) → x (clippy::needless_question_mark)
- Go: use http.NoBody instead of nil request body (gocritic::httpNoBody)

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

Author: whites11

flow/internal/env.go

@@ -105,7 +105,7 @@ func decryptWithAwsKms(ctx context.Context, data []byte, keyID string) ([]byte,
 func decryptWithGcpKms(ctx context.Context, data []byte, keyID string) ([]byte, error) {
 	// Get access token from GKE Workload Identity metadata server
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet,
-		"http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token", nil)
+		"http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token", http.NoBody)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create metadata request: %w", err)
 	}

nexus/catalog/src/lib.rs

@@ -131,7 +131,7 @@ async fn gcp_kms_decrypt(encrypted_payload: &str, kms_key_id: &str) -> anyhow::R
         .decode(plaintext_b64)
         .context("failed to decode GCP KMS plaintext")?;
 
-    Ok(String::from_utf8(plaintext).context("GCP KMS plaintext is not valid UTF-8")?)
+    String::from_utf8(plaintext).context("GCP KMS plaintext is not valid UTF-8")
 }
 
 #[cfg(not(feature = "gcp"))]