fix: resolve exported type stuttering issues (revive)

- Rename VaultMetadata to Metadata in internal/vault package to avoid stuttering
- Rename BIP85DRNG to DRNG in pkg/bip85 package to avoid stuttering
- Update all references in code and tests

pkg/agehd/agehd_test.go

@@ -393,6 +393,7 @@ func TestIdentityFromEntropyEdgeCases(t *testing.T) {
 						err,
 					) // In test context, panic is acceptable for setup failures
 				}
+
 				return b
 			}(),
 			expectError: false,