Remove detected.init_store() in Location.__init__

[will-moore]

Fixes #445.

We no-longer need to create a new store since #413 the store is the same for all subclasses of ome_zarr.format.Format.

Just 1 test failed test_astronaut_download() and this was fixed by download() using the detected zarr_format for writing.

This is potentially quite a big change (hence the Draft status) - Need to consider if that test failure should be fixed in a better way etc.
Do we need the Format class hierarchy any more? Is there a better way to handle format differences?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.54%. Comparing base (2eec589) to head (948c6a0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #468      +/-   ##
==========================================
- Coverage   86.99%   86.54%   -0.46%     
==========================================
  Files          13       13              
  Lines        1769     1761       -8     
==========================================
- Hits         1539     1524      -15     
- Misses        230      237       +7     

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