Unpacker: Change max_buffer_size to 100MiB

[methane]

No description provided.

[codecov-io]

Codecov Report

Merging #391 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #391      +/-   ##
========================================
+ Coverage   87.99%    88%   +0.01%     
========================================
  Files           5      5              
  Lines         808    809       +1     
========================================
+ Hits          711    712       +1     
  Misses         97     97

Impacted Files	Coverage Δ
msgpack/fallback.py	89.06% <100%> (+0.03%)	⬆️
msgpack/ext.py	82.81% <0%> (-0.27%)	⬇️

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