add pathfinder dataset

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Add LRA Pathfinder dataset to meerkat.

To avoid tensorflow dependencies, we have preprocessed the dataset. The preprocessed dataset is fetched with meerkat

Reference:
https://github.com/google-research/long-range-arena

[codecov-commenter]

Codecov Report

Merging #317 (61f2dd8) into main (86dfb17) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #317   +/-   ##
=======================================
  Coverage   67.38%   67.38%           
=======================================
  Files         211      211           
  Lines       11943    11943           
  Branches     1787     1787           
=======================================
  Hits         8048     8048           
  Misses       3469     3469           
  Partials      426      426           

Flag	Coverage Δ
unittests	67.38% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
meerkat/ops/merge.py	77.27% <100.00%> (ø)

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