Needed mutation detection improvements

[iisakkirotko]

With #595 merged, We'll move these todo items from the PR to issues as a reminder to look at them before releasing Solara 2.0.

TODO:

• Trigger calls to check_mutations() from several places: after an event handler (requires a change in reacton) and after a component run.
• We probably do not want two equals function in solara/reacton, reconcile this.
• Give an option to opt out of the mutation check per reactive var (e.g. when equals fails), or for performance reasons. #983
• support reactive.get(copy=True) to always get a copy, even when _CHECK_MUTATIONS is False
• Do we need support reactive.get(reference=True) to always get a reference, or is the opt-out enough?