feat: add --submodel to perf and build commands

[xieofxie]

Summary

Expands the --submodel capability (added to winml export in #1031) to the winml perf and winml build commands, letting users select a single sub-model of a composite model instead of processing all of them.

Changes

winml build (build.py)

• Adds --submodel <name> option.
• After the existing resolve_composite_components() detection, validates and filters the components dict, mirroring export:
  • --submodel on a non-composite model → BadParameter ("not a composite model").
  • Unknown name → BadParameter listing available sub-models.
  • Otherwise narrows the fan-out to just that one sub-model build.

winml perf (perf.py)

• Adds --submodel <name> option and BenchmarkConfig.submodel field.
• perf detects composites post-load, so _run_sub_models() filters the loaded sub_models dict to the requested name (unknown → UsageError), and run() errors when --submodel is passed for a non-composite model.

Tests

• TestBuildSubmodel: filters to one component, rejects unknown name, rejects non-composite.
• TestPerfSubmodelFilter: benchmarks only the requested sub-model, runs only that session, rejects unknown name, rejects non-composite.

Verification: ruff clean, mypy clean on both modules; build/perf-composite (119) and perf-cli (68) tests pass.