chore: drop dead experiment-scaffold references

- Remove the pytest collect_ignore_glob that skipped WIP scaffolds
  (test_experiments / test_unet_conversion / standalone_test). Those
  files no longer exist and only imported the experimental
  coreml_suite.experiments / convert_apple modules.
- Drop .gitignore entries for the removed experiment and alternate-env
  directories (experiments/, experiment_results/, apple_env/, comfy_env/,
  coremlsuite-venv/).

.gitignore

@@ -1,11 +1,6 @@
 playground/
-experiments/
 __pycache__/
 models/
 .venv/
-apple_env/
-comfy_env/
-coremlsuite-venv/
-experiment_results/
 test_results/
 tests/m2/_latest_generated.png

tests/conftest.py

@@ -5,8 +5,6 @@
   this package's root.
 - Auto-applies tier markers based on the directory a test lives in, so
   individual files don't have to repeat @pytest.mark.unit / .m2.
-- Skips in-progress test scaffolds so they don't break collection (they
-  reference modules / venv layouts that aren't part of this suite).
 """
 import sys
 from pathlib import Path
@@ -21,15 +19,6 @@ for p in (str(COMFY_DIR), str(REPO_ROOT)):
         sys.path.insert(0, p)
 
 
-# Skip WIP test scaffolds; they import modules (coreml_suite.experiments,
-# convert_apple) that are not part of this suite.
-collect_ignore_glob = [
-    "unit/test_experiments.py",
-    "unit/test_unet_conversion.py",
-    "unit/standalone_test.py",
-]
-
-
 _TIER_BY_DIR = {
     "tests/unit": "unit",
     "tests/m2": "m2",