Add models and routes for reporting dataset lookup errors

[ponyisi]

Companion to ssl-hep/ServiceX_DID_Finder_lib#38 . Adds a new dataset lookup failure endpoint and updates models as necessary. Still missing an endpoint to query what the error was (for client information) and tests.

[Copilot]

Pull Request Overview

This PR adds functionality to handle and report dataset lookup errors in the ServiceX application. It introduces a new endpoint for receiving error notifications from the dataset lookup service and updates the data models to support error tracking.

• Adds a new /servicex/internal/transformation/<dataset_id>/error endpoint for reporting dataset lookup failures
• Extends the DatasetStatus enum with three new error states: does_not_exist, bad_name, and internal_failure
• Adds a new TransformStatus.bad_dataset state to mark transformations that fail due to dataset issues

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
servicex_app/routes.py	Registers the new FilesetError resource and endpoint
servicex_app/resources/internal/fileset_error.py	Implements the error handling endpoint with dataset status updates and transformation cleanup
servicex_app/models.py	Extends DatasetStatus and TransformStatus enums with new error states

[ponyisi]

Actually we already have the endpoint for querying dataset status so all that's needed is the tests

[gordonwatts]

But wait - where are the tests?

[ponyisi]

Complete, Gordon signed off offline