Pass through model.rgn in agent analogous to model.random

[quaquel]

This is a follow up PR from #2352. It adds a new property to Agent: Agent.rng. Implementation wise it is identical to Agent.random. This PR also explicitly adds tests for both properties.

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
BoltzmannWealth	small	🔵 +1.6% [+0.8%, +2.3%]	🔵 -0.1% [-0.3%, +0.2%]
BoltzmannWealth	large	🔵 +0.2% [-0.4%, +0.7%]	🔵 -0.3% [-0.8%, +0.2%]
Schelling	small	🔵 +0.0% [-0.3%, +0.4%]	🔵 +0.0% [-0.4%, +0.4%]
Schelling	large	🔵 +0.1% [-0.3%, +0.6%]	🔵 +0.8% [-0.3%, +1.9%]
WolfSheep	small	🔵 +0.5% [+0.3%, +0.6%]	🔵 -0.0% [-0.2%, +0.2%]
WolfSheep	large	🔵 +1.0% [+0.3%, +1.7%]	🔵 +0.5% [-0.1%, +1.1%]
BoidFlockers	small	🔵 -1.0% [-1.7%, -0.2%]	🔵 -1.8% [-2.5%, -1.1%]
BoidFlockers	large	🔵 -0.2% [-0.5%, +0.2%]	🔵 -2.0% [-2.6%, -1.4%]

[EwoutH]

Very clean and consistent with the Model implementation