move all m.* functions to use m.act

[jakelorocco]

m.act is the default implementation of how a session interacts with a backend. All other m.* functions (besides validate) will call that function and do pre/post processing to get the same results as before.

Notes:

• m.validate can't use act since requirements directly call the backend.generate functions; we can "fix" this if we have requirements take MelleaSession objects
• act handles context additions; this means that query and transform no longer handle adding to context differently depending on the context
• tool calling for transform will get moved in a future PR (there are no regressions here)

All tests pass.

[jakelorocco]

I've messed up the refs here by pulling in main while building off hen/sampling_strategy_new. Will need to wait for that PR.

[jakelorocco]

I've fixed the refs; final changes:

• added generic capabilities to m.act
• m.* functions use m.act under the hood
• removed m.genslot since that's identical to m.act
• fixed a few small things in the sampling file
• added overloads to m.act and m.instruct so that return types aren't unions

All tests pass (ran locally).

[HendrikStrobelt]

LGTM