eval: add inventory coding task coverage

[CuSO41108]

Summary

• add an isolated inventory_service fixture with passing seed tests
• add seven deterministic coding tasks covering boundaries, new APIs, atomic batches, compatibility, formatting, and code/test/docs changes
• expand the built-in Eval v2 suite from 28 to 35 cases

Verification

• python -m unittest tests.unit.test_evals tests.unit.test_eval_runtime_integration tests.unit.test_openai_compatible -v (39 passed)
• python -m unittest discover -s evals/fixtures/inventory_service/tests -v (4 passed)
• git diff --check

Local live-model Smoke

• inventory_low_stock_boundary_001: passed all task, behavior, file-change, and trajectory checks
• inventory_reserve_many_001: implementation and independent verification passed, but the Agent hit max_tool_rounds_exceeded before self-verification/final response
• inventory_document_default_threshold_001: all code/test/README verification passed, but the Agent hit the same process limit before self-verification/final response

The two failures are retained as capability evidence; their Oracles were not weakened. No credentials, model configuration, or live artifacts are included.

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