Cleanup PALC Cache

[GrantHecht]

Currently, we use a single PALCCache struct to store the current state of the PALC method and preallocated memory. While this works, certain parts of this cache are very specific to either the prediction or correction steps, it makes understanding what parts of the cache are modified in different parts of the algorithm difficult. As such, I think we should define some new cache structs specifically for the prediction and correction steps to cleanup this part of the code a bit.

At a high level, this could look something like:

mutable struct PALCPredictionCache 
    # Prediction specific data/info/allocated memory
end

mutable struct PALCCorrectionCache
    # Correction specific data/info/allocated memory
end

mutable struct PALCCache
    # Data/info/allocated memory used in both steps
     prediction_cache::PALCPredictionCache
     correction_cache::PALCCorrectionCache
end