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/vault/vault.go

@@ -30,6 +30,7 @@ func NewVault(fs afero.Fs, stateDir string, name string) *Vault {
 		longTermKey: nil,
 	}
 	secret.Debug("Created NewVault instance successfully")
+
 	return v
 }
 
@@ -92,6 +93,7 @@ func (v *Vault) GetOrDeriveLongTermKey() (*age.X25519Identity, error) {
 				"derived_hash", derivedPubKeyHash,
 				"stored_hash", metadata.PublicKeyHash,
 				"derivation_index", metadata.DerivationIndex)
+
 			return nil, fmt.Errorf("derived public key does not match vault: mnemonic may be incorrect")
 		}
 
@@ -178,7 +180,8 @@ func (v *Vault) GetOrDeriveLongTermKey() (*age.X25519Identity, error) {
 
 	// Cache the derived key by unlocking the vault
 	v.Unlock(ltIdentity)
-	secret.Debug("Vault is unlocked (lt key in memory) via unlocker", "vault_name", v.Name, "unlocker_type", unlocker.GetType())
+	secret.Debug("Vault is unlocked (lt key in memory) via unlocker",
+		"vault_name", v.Name, "unlocker_type", unlocker.GetType())
 
 	return ltIdentity, nil
 }