Refactor `INTMinTree` to return a `Vec<Entry>`

[ariasanovsky]

Currently, we make expensive key clones. With the BTreeMap tree, this is necessary to avoid having a & to data under a &mut.

The cost of this is high, including many temporary Vec's (c.f. ActionsTaken).

To resolve this:

• [x] replace the BTreeMap with a Vec<BTreeMap>, preserving identical behavior
• [x] refactor INTTransitions to hold a Vec<Entry> instead of Vec<(ActionsTaken, ...)>
• [x] make an Issue to manage action/state space exhaustion

[ariasanovsky]

refactor INTTransitions to hold a Vec instead of Vec<(ActionsTaken, ...)> Used a Vec<(&mut StateData, ...)> instead due to Entry semantics.