Fix pynwb.validate() for Zarr-backed NWB files

[h-mayorquin]

I encounter this while working on the inspector NeurodataWithoutBorders/nwbinspector#699

Closes #2131 and #2119.

Calling pynwb.validate() on a Zarr file raised TypeError: ZarrIO.load_namespaces: unrecognized argument: 'driver', unrecognized argument: 'aws_region' because the validator resolved the backend via _get_backend and then unconditionally forwarded HDF5 (Hierarchical Data Format 5) kwargs (driver, aws_region, load_namespaces) into whichever backend it returned, including NWBZarrIO.

The fix follows, to the best of my understanding, @oruebel recommendation here in hdmf-dev/hdmf-zarr#302: rather than scatter backend dispatch across the validator, concentrate backend-specific construction in a single _open_backend_io helper that translates kwargs per backend, and switch namespace loading to HDMFIO.load_namespaces_io on the open IO. This leverages @rly's instance-method API added in hdmf-dev/hdmf#1299 which replaces the classmethod call that required reaching into the private io._file attribute, so the long-standing TODO from #2119 is retired as part of the same change. storage_options is added to the public validate() API so Zarr users can pass fsspec (filesystem spec) config through.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.19%. Comparing base (9231882) to head (db00200).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #2187      +/-   ##
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+ Coverage   95.18%   95.19%   +0.01%     
==========================================
  Files          30       30              
  Lines        2991     2999       +8     
  Branches      444      445       +1     
==========================================
+ Hits         2847     2855       +8     
  Misses         86       86              
  Partials       58       58              

Flag	Coverage Δ
integration	73.12% <100.00%> (+0.07%)	⬆️
unit	85.66% <95.23%> (+0.07%)	⬆️

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