test(config): add unit tests for BuildNameFilterFn

[shihyunhuang]

Description
This PR adds unit tests for BuildNameFilterFn in core/config/model_config_filter.go.
BuildNameFilterFn is called by the GET /v1/models endpoint to filter the model list by name regex. Despite being used across several API handlers, the function had no test coverage.
The three test cases cover:

• Empty filter string returns a pass-all filter (no error)
• Invalid regex returns an error and a nil function (prevents panic in callers)
• Valid regex correctly matches models by name

Notes for Reviewers
No behaviour changes — tests only. The new file is core/config/model_config_filter_test.go.

Signed commits

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