Disable MA map pre-generation in CorrelationDecoder

[tsalo]

Closes None, but should help many users. Per #629 and #630, storing the MA maps as files and loading them as needed actually slows things down and increases memory usage, which could, at least in part, explain why CorrelationDecoder is so unusable for users.

Changes proposed in this pull request:

• Do not pre-generate MA maps for the CorrelationDecoder.
• Also, use tqdm to track the decoder's fit progress.

[codecov]

Codecov Report

Merging #637 (636a7c5) into main (c35ca9b) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #637      +/-   ##
==========================================
- Coverage   87.89%   87.86%   -0.03%     
==========================================
  Files          40       40              
  Lines        4320     4319       -1     
==========================================
- Hits         3797     3795       -2     
- Misses        523      524       +1     

Impacted Files	Coverage Δ
nimare/decode/continuous.py	94.94% <100.00%> (-0.06%)	⬇️
nimare/meta/kernel.py	96.51% <0.00%> (-0.59%)	⬇️

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