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.test.ts

@@ -72,7 +72,6 @@ describe('proxyInputFileResolver', () => {
             file_id: 'file-metapi-123',
             filename: 'brief.pdf',
             file_data: Buffer.from('%PDF-local').toString('base64'),
-            mime_type: 'application/pdf',
           },
         ],
       },