Unit test ReportFileStorageClient upload and signed URL

Supabase Flutter's storage client (`supabase.storage.from(bucket)`) returns a `StorageFileApi`. The upload method signature and progress streaming vary between supabase_flutter versions — check `pubspec.lock` for the exact version before writing mocks. In newer versions, progress is reported via an `onUploadProgress` callback rather than a Stream. If so, capture the callback in the mock and call it with a synthetic `StorageUploadProgress` object to verify the client handles it.

For path construction, define the expected convention as a constant or helper in the client class itself (e.g., `_buildPath(orgId, reportId, filename)`), which makes it independently testable with a simple unit test that doesn't need mocks. Wrap all storage API calls in try/catch converting `StorageException` to a domain exception — keep the error wrapping in a single private method `_handleStorageError()` to avoid repetition across methods.

Pure unit tests using Mockito mocks for `SupabaseStorageClient` and `StorageFileApi`. For the progress stream test, use a `StreamController` and emit synthetic progress events from the mock, then assert the stream received them via `expectLater(stream, emitsInOrder([...]))`. For path construction tests, use `verify(mockStorageApi.uploadBinary(captureAny, ...))` and assert the captured path matches the expected pattern. For error wrapping tests, configure the mock to throw `StorageException` and verify the client catches it and throws the domain-level equivalent.

Test file: `report_file_storage_client_test.dart` under `test/unit/clients/`. Group tests by method name for clarity.