refactor: fold _perf_modules into PerfBenchmark

Summary

winml perf --module is handled by a standalone _perf_modules() function in src/winml/modelkit/commands/perf.py, separate from the PerfBenchmark class used for single-model and composite runs. The two paths duplicate build + benchmark orchestration (input generation, session compile, monitored/simple loops, HW monitor wiring, result collection) and have already drifted (e.g. device/EP resolution lives in different places).

Motivation

While fixing #931 (perf with no --ep should target one concrete EP, not aggregate all), device/EP resolution was moved inside PerfBenchmark (it resolves config.device/config.ep at the start of _load_model, failing fast before the build). The --module path still resolves the EP in the CLI perf() function because _perf_modules is not part of PerfBenchmark. This leaves a transitional duplication:

• PerfBenchmark._resolve_device_ep() — single-model / composite
• inline resolve_device/resolve_eps block in perf()'s module branch — per-module

Proposal

Fold per-module benchmarking into PerfBenchmark so there is a single orchestration path:

• A per-module mode on PerfBenchmark (or a small subclass) that builds each submodule ONNX and benchmarks it through the same input-gen / compile / loop / collect machinery used for single models.
• Remove the standalone _perf_modules() and the duplicated device/EP resolution in the CLI module branch — the CLI just constructs the benchmark and runs it.
• Reuse _run_monitored_loop / _run_simple_loop and result collection instead of the parallel implementations currently in _perf_modules.

Acceptance

• winml perf --module <Class> produces the same per-instance table + JSON report.
• Device/EP resolution happens in exactly one place (PerfBenchmark).
• Existing tests/unit/commands/test_perf_module.py passes (adjusted only for the new call path).

References

• Follow-up to #931.
• Code marker: comment in perf()'s --module branch in src/winml/modelkit/commands/perf.py points here.