[FEATURE] Investigate Adding a Variant Based Implementation

[DeveloperPaul123]

After a discussion on my discord with a user, it came up that there may be some easy performance gains by using std::variant instead of std::any with std::any_cast. I'd like to investigate looking into using this as an alternative implementation of the event bus and then allow users to opt in (or out) of a particular implementation using a policy or something similar.

There should also be a benchmark to compare the performance between the two implementations (mostly to see how long event dispatch takes).

[DeveloperPaul123]

@games-on-whales has implemented an initial version of the variant version here: https://github.com/games-on-whales/eventbus