Update multiagent vs. union performance docs for Julia 1.11

[Tortar]

The new timings are much more similar in 1.11, see https://juliadynamics.github.io/Agents.jl/dev/performance_tips/#multi_vs_union. But @multiagent has still the edge

[Tortar]

The last commit makes the benchmark not allocating, @multiagent is now 2x faster than a union on that for Julia 1.11

[Datseris]

I've been seeing performance regressions all across the board with 1.11. In compile time and run time... I suggest that we wait for 1.11.1 fix first before considering this seriously.

[Tortar]

that seems good to me, but I'm skeptical about that making a big difference in compile times, I think it will take more than 1 release to improve this substantially, run times seems better to me on 1.11 instead

[Tortar]

1.11.1 is out and it didn't improve much the state of Julia 1.11 release, I think it will take a fair amount of time to fix the compile issues of 1.11

[Datseris]

ah, damn, to move to 1.11 we need to change OSM Visualizations, that's where teh failure comes from.