Conventions around continuous MDP descriptions

[sbenthall]

These are features that are of interest to HARK that are not yet supported in Dolo, that are high priority according to @llorracc

1. "Cycles" in which the agents solve a different problem in each subperiod
2. Finite Horizons specification of the SolvingMicroDSOPs life cycle model that has age-varying magnitudes of transitory and permanent shocks, income growth, and other inputs
3. "Absolute time" A way to make reference to some absolute time (like, what year is it, in addition to what age am I). This is much less important, and if hard to do could be dropped
4. Conventions for how to keep track of agents who are "ex-ante" heterogeneous so that we can develop tools for handling such populations efficiently.

We should work with @albop to come up with conventions for describing these in Dolang YAML, Python, or both.

[sbenthall]

#563 <-- previous discussion about cycles

c	t	t$v, a, ('a','b')
	period	sub period
cycle	sub cycle
		frame

[sbenthall]

(1) is addressed by #1186

(4) is addressed by SHARKFin AgentPopulations