fix(copilot): include copilot legacy chat sessions

[JaylyDev]

Summary

Adding support for VS Code's GitHub Copilot chat sessions prior to February 2026 to copilot's parser.

How it works:

The parser scan for chatSessions/*.json and parses the legacy chat sessions if there is a requests array in root JSON object. The schema of those JSON files and its definitions like IToolCallRound and ThinkingData can be found in https://github.com/microsoft/vscode-copilot-chat.

This old format reads all of input, output, reasoning messages and tool calling outputs to determine number of tokens used by a model, which is also stored in the request object. It reads exact token counts (promptTokens, completionTokens, usage) when available, otherwise it fallbacks to character-based estimation.

This parser also maps the model used in auto model selection to the actual model used.

Testing

• I have tested this locally against real data (not just unit tests)
• npm test passes
• npm run build succeeds

For new providers only:

• I installed the tool and generated real sessions by using it
• npm run dev -- today shows correct costs and session counts for this provider
• npm run dev -- models --provider <name> shows correct model names and pricing
• Screenshot or terminal output attached below proving it works with real data

Before:

After: