Use new VoronoiGrid discrete space in examples

This issue aims to create an example with the functionalities of VoronoiGrid discrete space and its main applications.

- Original Mesa Issue: https://github.com/projectmesa/mesa/issues/1895
- Original PR: https://github.com/projectmesa/mesa/pull/2084

Most Voronoi applications involve continuous space moving agents. Here, using discrete space, the main ideia is to model [John Snow Cholera](https://en.wikipedia.org/wiki/John_Snow#Cholera) using the VoronoiGrid this way:

- Each cell have one pump and a certain amount of people
- Pumps can contaminate neighbor pumps or people in the cell
- People can move between cells
- Pumps can be closed/fixed

We assign probabilities to the events (moving around, contaminating) and simulate in order to analyze how important interventions (closing or fixing pumps) are.

This is just an ideia for the example, suggestions are welcome.

### References
- [R Package for Analyzing John Snow's 1854 Cholera Map ](https://github.com/lindbrook/cholera)
- [Why this pattern shows up everywhere in nature | Voronoi Cell Pattern](https://www.youtube.com/watch?v=GafRRl5XRPM&t=183s)
- [NetLogo](http://ccl.northwestern.edu/netlogo/models)

Start by reviewing the linked original Mesa issue and pull request, then inspect existing mesa-examples and the VoronoiGrid API. Done means adding a documented example that models cells, pumps, people, movement, contamination, and pump interventions, with a simulation that demonstrates their effects.

Written by the indexing model from the issue text.