Change pd_grid example to use create_agents

[quaquel]

This modifies the prisoner dilemma example to use create_agents instead of a for loop.

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
BoltzmannWealth	small	🔵 +0.6% [-0.4%, +1.6%]	🔵 +0.6% [+0.4%, +0.7%]
BoltzmannWealth	large	🔵 +0.6% [-0.1%, +1.4%]	🔵 +1.3% [-0.2%, +2.8%]
Schelling	small	🔵 +0.7% [+0.3%, +1.1%]	🔵 +0.8% [+0.5%, +1.1%]
Schelling	large	🔵 +0.9% [+0.6%, +1.2%]	🔵 +0.5% [-0.3%, +1.5%]
WolfSheep	small	🔵 +1.0% [+0.6%, +1.2%]	🔵 +3.5% [+2.2%, +4.7%]
WolfSheep	large	🔵 -0.1% [-1.5%, +1.5%]	🔵 +0.3% [-4.0%, +5.2%]
BoidFlockers	small	🔵 -1.6% [-2.1%, -1.2%]	🔵 -0.3% [-0.8%, +0.3%]
BoidFlockers	large	🔵 -2.1% [-3.8%, +0.7%]	🔵 +0.1% [-0.6%, +1.0%]

[tpike3]

LGTM