[wip] Offline overlap-based protocol rebalancing

[maxentile]

Currently TM has a few methods for adapting the number and spacing of lambda windows along a fixed path, depending on the setting:

• greedy bisection : starts with no samples between 0<lam<1, finds a sequence of lams such that overlap(lams[i], lams[i+1]) > threshold. ( https://github.com/proteneer/timemachine/pull/959 )
• adaptive smc : starts with no samples at lam>0, finds a sequence of lams such that ~ chi2_div(lams[i], lams[i+1]) ~= threshold ( https://github.com/proteneer/timemachine/pull/1177 )
• offline "rebalancing" : starts with samples that allow reweighting to any lam between 0 and 1, finds a sequence of lams such that heuristic_dist(lams[i], lams[i+1]) ~= threshold ( https://github.com/proteneer/timemachine/pull/538 )

This PR will extend the offline "rebalancing" functionality, with the intent of compressing the output of greedy bisection. (Motivation: bisection guarantees that the estimated overlap(lams[i], lams[i+1]) > threshold, but does not minimize len(lams).)

[maxentile]

Optimization approach needs work, will revisit after the more immediately usable utilities https://github.com/proteneer/timemachine/pull/1387