Unify getters

[odunbar]

Issue

We still have many floating ekp. and uki. notations rather than proper get methods.
E.g.
https://github.com/CliMA/EnsembleKalmanProcesses.jl/blob/fb45f75fa510691ded6f094a41bb85b4f408253d/src/EnsembleKalmanInversion.jl#L125C48-L125C59
We are working on this but here is a list of some yet to be done:

Solution

Replacing ekp. with get_...(ekp).

Where

Tasks

Beta Give feedback

1. \Delta t and \Delta t [end]
2. rng
3. all the uki internals...
4. obs_mean and obs_noise_cov
5. failure handler
6. all the sparse eki internals...