feat(metadata): implement metadata providers and initialize metadata service

- Added ModelMetadataProvider and CivitaiModelMetadataProvider for handling model metadata.
- Introduced SQLiteModelMetadataProvider for SQLite database integration.
- Created metadata_service.py to initialize and configure metadata providers.
- Updated CivitaiClient to register as a metadata provider.
- Refactored download_manager to use the new download_file method.
- Added SQL schema for models, model_versions, and model_files.
- Updated requirements.txt to include aiosqlite.

refs/civitai.sql

@@ -0,0 +1,38 @@
+CREATE TABLE models (
+            id         INTEGER PRIMARY KEY,
+            name       TEXT NOT NULL,
+            type       TEXT NOT NULL,
+            username   TEXT,
+            data       TEXT NOT NULL,
+            created_at INTEGER NOT NULL,
+            updated_at INTEGER NOT NULL
+        ) STRICT;
+CREATE TABLE model_versions (
+            id           INTEGER PRIMARY KEY,
+            model_id     INTEGER NOT NULL,
+            position     INTEGER NOT NULL,
+            name         TEXT NOT NULL,
+            base_model   TEXT NOT NULL,
+            published_at INTEGER,
+            data         TEXT NOT NULL,
+            created_at   INTEGER NOT NULL,
+            updated_at   INTEGER NOT NULL
+        ) STRICT;
+CREATE INDEX model_versions_model_id_idx ON model_versions (model_id);
+CREATE TABLE model_files (
+            id               INTEGER PRIMARY KEY,
+            model_id         INTEGER NOT NULL,
+            version_id       INTEGER NOT NULL,
+            type             TEXT NOT NULL,
+            sha256           TEXT,
+            data             TEXT NOT NULL,
+            created_at       INTEGER NOT NULL,
+            updated_at       INTEGER NOT NULL
+        ) STRICT;
+CREATE INDEX model_files_model_id_idx ON model_files (model_id);
+CREATE INDEX model_files_version_id_idx ON model_files (version_id);
+CREATE TABLE archived_model_files (
+            file_id INTEGER PRIMARY KEY,
+            model_id INTEGER NOT NULL,
+            version_id INTEGER NOT NULL
+        ) STRICT;