Remove JupyterViz Altair marker overlap for huge grid size

[rht]

This is #2049, but for the Altair visualization instead.
20x20

60x60

100x100

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
Schelling	small	🔵 -0.5% [-0.8%, -0.2%]	🔵 -0.1% [-0.3%, +0.0%]
Schelling	large	🔵 +0.2% [-0.3%, +0.6%]	🔵 +0.2% [-0.7%, +1.2%]
WolfSheep	small	🔵 -0.4% [-0.6%, -0.2%]	🔵 -0.1% [-0.2%, +0.0%]
WolfSheep	large	🔵 +0.8% [+0.0%, +1.7%]	🔵 +1.8% [+0.8%, +2.7%]
BoidFlockers	small	🔵 -0.9% [-1.4%, -0.4%]	🔵 +1.4% [+0.9%, +2.0%]
BoidFlockers	large	🔵 -1.1% [-1.6%, -0.7%]	🔵 +1.0% [+0.6%, +1.4%]

[quaquel]

LGTM