feat(tests): enhance modelTesterSession tests and add proxy logs tests

- Updated modelTesterSession tests to serialize assistant history as output_text and removed mime_type from input_file.
- Introduced new tests for stats proxy logs routes, covering paginated log retrieval and detailed log views with parsed billing details.
- Added server-driven tests for ProxyLogs component to validate API interactions and UI rendering based on server data.

src/server/services/proxyInputFileResolver.ts

@@ -214,7 +214,6 @@ function toResponsesResolvedBlock(file: { fileId?: string; filename: string; fil
     ...(file.fileId ? { file_id: file.fileId } : {}),
     filename: file.filename,
     file_data: file.fileData,
-    mime_type: file.mimeType,
   };
 }