breaking: Remove visualization_old (mesa-viz-tornado)

[rht]

TODO:

• Merge Remove mesa.flat namespace #2091.
• Update cookiecutter template.

[rht]

This fixes the tests.

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
Schelling	small	🔵 -0.1% [-0.4%, +0.1%]	🔵 -0.7% [-1.0%, -0.5%]
Schelling	large	🔵 -0.9% [-1.6%, -0.2%]	🔵 -2.0% [-2.9%, -1.2%]
WolfSheep	small	🔵 -0.3% [-1.4%, +0.9%]	🔵 -1.1% [-1.4%, -0.8%]
WolfSheep	large	🔵 -1.3% [-2.0%, -0.5%]	🔵 -2.3% [-3.9%, -0.7%]
BoidFlockers	small	🔵 -0.1% [-0.8%, +0.6%]	🔵 -0.7% [-1.3%, -0.1%]
BoidFlockers	large	🔵 -1.4% [-2.1%, -0.6%]	🔵 -0.3% [-1.1%, +0.3%]

[EwoutH]

Personally, I'm going to approve this. Let's cut the cord and focus on the future. The new space needs some work (like support for Cell spaces and PropertyLayers) but it's the future.

I would like more maintainers to pitch in and/or approve (at least a second) before merging though, since this is a big change.