Remove unnecessary obstore import

[maxrjones]

Call store.get_range_async(...) rather than obstore.get_range_async(store, ...)

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 89.39%. Comparing base (46aeaea) to head (7f98f1a).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #599      +/-   ##
===========================================
- Coverage    89.40%   89.39%   -0.01%     
===========================================
  Files           34       34              
  Lines         1944     1943       -1     
===========================================
- Hits          1738     1737       -1     
  Misses         206      206              

Files with missing lines	Coverage Δ
virtualizarr/manifests/store.py	91.97% <100.00%> (-0.05%)	:arrow_down:

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