refactor: remove unused MappingPath from FactCheckModelConfig

[Xunzhuo]

Remove the unused MappingPath field from FactCheckModelConfig as the fact-check classifier loads label mappings directly from the model's config.json file, consistent with hallucination and NLI models.

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[github-actions]

Performance Benchmark Results

Component benchmarks completed successfully.

Summary

• Classification benchmarks: ✅
• Decision engine benchmarks: ✅
• Cache benchmarks: ✅

Details

See attached benchmark artifacts for detailed results and profiles.

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Performance testing powered by vLLM Semantic Router

[github-actions]

👥 vLLM Semantic Team Notification

The following members have been identified for the changed files in this PR and have been automatically assigned:

📁 bench

Owners: @yuezhu1, @Xunzhuo
Files changed:

• bench/hallucination/config-7b.yaml
• bench/hallucination/config.yaml

📁 config

Owners: @rootfs, @Xunzhuo
Files changed:

• config/prompt-guard/prompt_guard.yaml
• config/semantic-cache/config.redis.yaml
• config/testing/config.hallucination.yaml

📁 src

Owners: @rootfs, @Xunzhuo, @wangchen615
Files changed:

• src/semantic-router/pkg/classification/fact_check_classifier.go
• src/semantic-router/pkg/classification/hallucination_test.go
• src/semantic-router/pkg/config/config.go
• src/semantic-router/pkg/config/config_test.go
• src/semantic-router/pkg/config/helper.go

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This comment was automatically generated based on the OWNER files in the repository.