0.27.5 (step 2, item 2): rename provenance enum KeySource -> KeyOrigin

Disambiguates the key vocabulary: Key (the input handed to decrypt_with),
key sources (the resolver's lookup list), and KeyOrigin (how a key was
resolved). Internal-only rename — no dependents import it.

src/disc/encrypt.rs

@@ -454,12 +454,12 @@ impl Disc {
             mkb_version: mkb_ver,
             disc_hash: aacs::disc_hash_hex(&resolved.disc_hash),
             key_source: match resolved.key_source {
-                1 => KeySource::DeviceKey,
-                2 => KeySource::ProcessingKey,
-                3 => KeySource::KeyDbDerived,
-                4 => KeySource::KeyDb,
-                5 => KeySource::KeyDbUnitKeys,
-                _ => KeySource::KeyDb,
+                1 => KeyOrigin::DeviceKey,
+                2 => KeyOrigin::ProcessingKey,
+                3 => KeyOrigin::KeyDbDerived,
+                4 => KeyOrigin::KeyDb,
+                5 => KeyOrigin::KeyDbUnitKeys,
+                _ => KeyOrigin::KeyDb,
             },
             vuk: resolved.vuk,
             unit_keys: resolved.unit_keys,
@@ -522,7 +522,7 @@ impl Disc {
             bus_encryption,
             mkb_version: mkb_ver,
             disc_hash: aacs::disc_hash_hex(&dh),
-            key_source: KeySource::ExternalUk,
+            key_source: KeyOrigin::ExternalUk,
             vuk: None,
             unit_keys: vec![(1, unit_key)],
             read_data_key: handshake.and_then(|h| h.read_data_key),
@@ -585,7 +585,7 @@ impl Disc {
             bus_encryption,
             mkb_version: mkb_ver,
             disc_hash: aacs::disc_hash_hex(&dh),
-            key_source: KeySource::ExternalUk,
+            key_source: KeyOrigin::ExternalUk,
             vuk: None,
             unit_keys: vec![],
             read_data_key: handshake.and_then(|h| h.read_data_key),