Ignore Python __pycache__ directories

Running the new ch04_HelloCube.py exercise leaves a __pycache__/ folder
of compiled bytecode next to it, which showed up as untracked. The
pattern has no leading slash so it covers any Python exercise added
later.

No new point in the implementation plan and no version bump: this is
repository housekeeping, not a point of its own.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: hudrima1

.gitignore

@@ -97,3 +97,4 @@ Tester
 docs/html
 .clangd
 docs/doxygen-awesome-css/
+__pycache__/