Add simple test script for testing out widely branched transform hierarchies

[Wumpf]

With lots of entities ofc.
Which also means that it practically replaces many_entities/main.py

Added as a super simple eyeballing-based end-to-end perf test that I'm using to make sure we don't regress perf as we're working on extending the transform system.

As we know, many entities is marred by various avoidable perf issues, notably transform perf is bad but not significant right now 😭

Example runs illustrating this:

pixi run rerun-release --threads=1
pixi run -e py python tests/python/many_entity_transforms/main.py --transforms-only

pixi run rerun-release --threads=1
pixi run -e py python tests/python/many_entity_transforms/main.py

[github-actions]

Web viewer built successfully.

Result	Commit	Link	Manifest
✅	b972e64	https://rerun.io/viewer/pr/11437	+nightly +main

^{Note: This comment is updated whenever you push a commit.}