refactor(profiling): consolidate into single module

Unify the profiling subsystem into one file per reviewer request.

Before (4 files):
  src/lerobot/utils/profiling_utils.py        399 LOC
  scripts/ci/run_model_profiling.py           337 LOC
  profiling/model_profiling_specs.json        181 LOC
  tests/scripts/test_model_profiling.py       423 LOC

After (2 files):
  src/lerobot/utils/model_profiling.py        758 LOC — TrainingProfiler +
                                                       CI orchestrator +
                                                       POLICY_SPECS (inline)
  tests/test_model_profiling.py               315 LOC

Net: -267 LOC and 4 files → 2. All functionality preserved: per-step
forward/backward/optimizer timings, torch profiler tables + chrome
traces, deterministic-forward fingerprint, HF Hub result upload, and
the same CLI surface.

Changes:
- Collapse `_StepTimingCollector` into inline attributes on
  `TrainingProfiler` (no separate class).
- Drop `ProfilingSpec` dataclass; specs are plain dicts.
- Inline the JSON matrix as a module-level `POLICY_SPECS` dict —
  one less file to keep in sync with the training args.
- CI workflow invokes `python -m lerobot.utils.model_profiling` in
  place of the standalone script.
- Tests import `lerobot.utils.model_profiling` directly instead of
  loading a script-by-path. Removed JSON schema tests that no
  longer apply.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/model_profiling.yml

@@ -23,12 +23,10 @@ on:
       - feat/libero-benchmark
     paths:
       - .github/workflows/model_profiling.yml
-      - profiling/model_profiling_specs.json
-      - scripts/ci/run_model_profiling.py
       - src/lerobot/configs/train.py
       - src/lerobot/scripts/lerobot_train.py
-      - src/lerobot/utils/profiling_utils.py
-      - tests/scripts/test_model_profiling.py
+      - src/lerobot/utils/model_profiling.py
+      - tests/test_model_profiling.py
   workflow_dispatch:
     inputs:
       git_ref:
@@ -206,7 +204,7 @@ jobs:
                 fi
 
                 cmd=(
-                  uv run python scripts/ci/run_model_profiling.py
+                  uv run python -m lerobot.utils.model_profiling
                   --output_dir=/workspace/profiling-results
                   --hub_org=lerobot
                   --results_repo="${RESULTS_REPO}"