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

internal/cli/vault.go

@@ -244,7 +244,7 @@ func (cli *Instance) VaultImport(cmd *cobra.Command, vaultName string) error {
 	existingMetadata, err := vault.LoadVaultMetadata(cli.fs, vaultDir)
 	if err != nil {
 		// If metadata doesn't exist, create new
-		existingMetadata = &vault.VaultMetadata{
+		existingMetadata = &vault.Metadata{
 			CreatedAt: time.Now(),
 		}
 	}