Add ensure BZ2

[cthoyt]

This PR adds an ensure_open_bz2 function that works similarly to ensure_open_gz. It also exposed a new function for opening BZ2-compressed JSON, like the one available in hetionet.

[codecov-commenter]

Codecov Report

Merging #55 (c097cb8) into main (d84f24d) will increase coverage by 0.39%. The diff coverage is 84.21%.

@@            Coverage Diff             @@
##             main      #55      +/-   ##
==========================================
+ Coverage   65.01%   65.40%   +0.39%     
==========================================
  Files          10       10              
  Lines         906      925      +19     
  Branches      153      147       -6     
==========================================
+ Hits          589      605      +16     
- Misses        296      299       +3     
  Partials       21       21              

Impacted Files	Coverage Δ
src/pystow/__init__.py	100.00% <ø> (ø)
src/pystow/api.py	68.94% <62.50%> (-0.34%)	:arrow_down:
src/pystow/impl.py	72.28% <100.00%> (+1.19%)	:arrow_up:

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