chore: stop tracking Python .pyc artifacts; ignore them repo-wide

The package's __pycache__/*.pyc were committed (regenerated on every build,
churning diffs and risking stale bytecode). Untrack all 7, add Python cache
patterns to the root .gitignore, and drop the now-redundant interop/.gitignore
(the root rule covers it).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -9,6 +9,12 @@ build-tsan/
 .DS_Store
 compile_commands.json
 
+# Python build/cache artifacts
+__pycache__/
+*.py[cod]
+*.egg-info/
+.pytest_cache/
+
 # Local Claude Code agent state (memory, skills, etc.)
 .claude/
 build-tsan-d/

interop/.gitignore

@@ -1 +0,0 @@
-__pycache__/