Refactor PostgreSQL provider: multi-schema & async prep

- Refactor migrations and provider to use multiple PostgreSQL schemas, each matching a legacy SQLite database (activitylog, authentication, displaypreferences, library, users).
- All tables, foreign keys, and indexes are now schema-qualified; Down migration drops tables by schema.
- Provider ensures schemas exist before migrations; entities are mapped to correct schemas in OnModelCreating.
- Add support for max-pool-size, min-pool-size, and multiplexing connection options; update logging accordingly.
- VACUUM ANALYZE now runs per schema during scheduled optimization.
- TruncateAllTablesAsync now truncates tables with schema qualification.
- README updated with schema structure, new options, and multiplexing warnings.
- CacheDecorator now calls async repository methods using .GetAwaiter().GetResult(), with documentation.
- Lays groundwork for full async/await and multiplexing support in the database layer.

MediaBrowser.Controller/Entities/BaseItem.cs

@@ -1145,8 +1145,16 @@ namespace MediaBrowser.Controller.Entities
             {
                 Id = item.Id.ToString("N", CultureInfo.InvariantCulture),
                 Protocol = protocol ?? MediaProtocol.File,
-                MediaStreams = MediaSourceManager.GetMediaStreams(item.Id),
-                MediaAttachments = MediaSourceManager.GetMediaAttachments(item.Id),
+                // Note: Using GetAwaiter().GetResult() here as this method is synchronous by design.
+                // TODO: Consider making GetVersionInfo async in future refactoring.
+                MediaStreams = MediaSourceManager
+                    .GetMediaStreamsAsync(item.Id, CancellationToken.None)
+                    .GetAwaiter()
+                    .GetResult(),
+                MediaAttachments = MediaSourceManager
+                    .GetMediaAttachmentsAsync(item.Id, CancellationToken.None)
+                    .GetAwaiter()
+                    .GetResult(),
                 Name = GetMediaSourceName(item),
                 Path = enablePathSubstitution ? GetMappedPath(item, itemPath, protocol) : itemPath,
                 RunTimeTicks = item.RunTimeTicks,