inherit_param_estimates: revisit rounding and use matrix-handling PR

[barrettk]

We were recently made aware of the fact that final estimates as returned from model_summary() may not be suitable for specification via inherit_param_estimates() due to the possibility of rounding impacting positive-definiteness for matrix-type records. We currently round values on top of that too.

The open matrix-handling PR (#656) has a lot of handling for this type of thing (checks for positive definiteness before/after rounding, and attempts to make matrices positive-definite if not). Especially given that inherit_param_estimates() might start to get a lot more use via the upcoming bootstrap feature, I think we'll want to add some of those checks/corrections to here as well (currently only part of tweak_param_estimates())

[barrettk]

Though technically not related to the bootstrap feature, im adding the label of bootstrap to make sure we think about this around the same time as the release of this feature (can still be a subsequent release). cc @seth127