Improve flocking benchmark

[coderbeta1]

Changes Made:

1. Changed self.velocity to self.direction: Both Velocity and Speed are agent attributes. This leads to unnecessary confusion. So I changed velocity to direction
2. Seed: It is now not compulsory to give a seed value. This allows for easy randomness if needed.
3. Default values: Code will work even if model values are not given
4. General Changes: Made the code more descriptive for beginners

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
Schelling	small	🔵 +0.7% [+0.3%, +1.2%]	🔵 -0.4% [-0.6%, -0.2%]
Schelling	large	🔵 +12.4% [-17.6%, +54.6%]	🔵 -3.4% [-4.3%, -2.5%]
WolfSheep	small	🔵 -0.4% [-0.9%, +0.1%]	🔵 +0.1% [-0.1%, +0.3%]
WolfSheep	large	🔵 +17.3% [-0.3%, +42.0%]	🔵 +0.4% [-1.0%, +1.6%]
BoidFlockers	small	🔴 +6.7% [+5.7%, +7.5%]	🔵 +2.2% [+1.4%, +2.9%]
BoidFlockers	large	🔴 +6.1% [+5.7%, +6.6%]	🔵 +2.5% [+2.0%, +3.1%]

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
Schelling	small	🔵 +0.1% [-0.3%, +0.5%]	🔵 -0.1% [-0.3%, +0.1%]
Schelling	large	🔵 +11.3% [-19.9%, +51.4%]	🔵 -1.5% [-4.3%, +1.5%]
WolfSheep	small	🔵 -0.6% [-1.1%, -0.1%]	🔵 +0.1% [-0.2%, +0.3%]
WolfSheep	large	🔵 +14.7% [-2.6%, +38.8%]	🔵 -2.7% [-4.6%, -0.9%]
BoidFlockers	small	🔵 +2.1% [+1.6%, +2.7%]	🔵 -2.1% [-2.8%, -1.4%]
BoidFlockers	large	🔵 +2.4% [+1.8%, +3.0%]	🔵 +0.2% [-0.4%, +0.9%]

[rht]

I just saw the docstring says "headings" and this needs to be replaced with "directions" as well.

[rht]

@coderbeta1 thank you for the needed corrections and improvements to the examples so far.