Add rumor spread example with Solara visualization

[RodionOm]

-- Summary

This PR adds a small Solara-based rumor spread example to 'mesa-examples'



.

The model places agents on a 2D toroidal grid. A configurable number of agents initially know a rumor. Informed agents may spread the rumor to neighboring agents, while a recovery mechanism allows agents to forget the rumor and return to the uninformed state.

-- Features

• Solara-based interactive visualization
• Spatial grid view of rumor diffusion
• Time-series plot of informed agents
• Parameter controls for:
  • initial spreaders
  • infection strength
  • recovery rate

-- Behavior

The model demonstrates multiple regimes depending on parameter values:

• Extinction: low infection strength and/or high recovery lead the rumor to die out
• Equilibrium: balanced infection and recovery produce sustained fluctuations
• Saturation: high infection strength and low recovery lead to near-total spread

-- Motivation

I built this example while preparing for GSoC and learning Mesa hands-on. I wanted to create a compact, reproducible model that demonstrates parameter-dependent rumor diffusion behavior in a way that is easy to run and inspect.

-- Notes

This model is intentionally simple and designed as an educational example rather than a realistic social diffusion simulator.

[RodionOm]

Hi! Just a quick follow-up — happy to adjust anything or align the example with project guidelines if needed. Thanks!