feat: Add embedding model integration tests with CI workflow

[yehudit1987]

Add comprehensive test suite for embedding model infrastructure covering
concurrency, memory, and performance. Includes 29 integration tests,
GitHub Actions workflow, and complete documentation.

• Concurrency tests: race conditions, deadlocks, goroutine leaks
• Memory tests: leak detection, growth analysis, GC behavior
• Performance tests: throughput, latency, concurrent performance
• CI workflow with model downloads and automated testing
• Makefile targets: test-embedding, bench-embedding
• Comprehensive test documentation and helper utilities

Resolve issue: #715

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[github-actions]

👥 vLLM Semantic Team Notification

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

📁 Root Directory

Owners: @rootfs, @Xunzhuo
Files changed:

• .github/workflows/integration-tests-embedding.yml

📁 src

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

• src/semantic-router/test/integration/README.md
• src/semantic-router/test/integration/embedding_concurrency_test.go
• src/semantic-router/test/integration/embedding_memory_test.go
• src/semantic-router/test/integration/embedding_performance_test.go
• src/semantic-router/test/integration/embedding_test_helpers.go

📁 tools

Owners: @yuluo-yx, @rootfs, @Xunzhuo
Files changed:

• tools/make/build-run-test.mk

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🎉 Thanks for your contributions!

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

[rootfs]

@OneZero-Y PTAL, thanks

[yehudit1987]

Optional: HF_TOKEN Configuration

This PR's tests support graceful fallback and pass without HF_TOKEN (Qwen3-only mode).

To enable full Gemma model testing, maintainers can add HF_TOKEN as a repository secret after accepting the Gemma model license.

This enables the BenchmarkEmbedding_ModelComparison benchmark and validates both model paths.