Expose gateway errors in TS client

[chaance]

This PR refactors error handling in the TS client so that response errors more closely mirror those returned from the gateway. Errors that are properly handled can then be exposed directly to users with less obfuscation.

Closes https://github.com/tensorzero/tensorzero/issues/2168 and https://github.com/tensorzero/tensorzero/issues/1763

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[!IMPORTANT] Refactor TS client error handling to use TensorZeroServerError for clearer gateway error messages.

• Error Handling:
  • Introduces TensorZeroServerError in errors.ts to handle server errors with specific status codes and messages.
  • Replaces HttpError with TensorZeroServerError in tensorzero.ts for more detailed error handling.
  • Updates error handling in inference.ts, route.tsx, and tensorzero.server.ts to use isTensorZeroServerError() for checking server errors.
• Code Refactoring:
  • Moves tensorzero.ts to tensorzero/tensorzero.ts and updates imports accordingly.
  • Removes ServerRequestError and isServerRequestError() from common.ts.
• Dependencies:
  • Adds http-status-codes to package.json for standardized HTTP status codes.

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