Fix validation in NWB testing util classes

[rly]

Motivation

The validate function in the pynwb.testing.testh5io classes was not validating the exported file and was using the older pynwb_validate(io=io) which validates against the core namespace instead of all leaves of the namespace hierarchy if extensions are present. The newer pynwb_validate(paths=[...]) syntax should be used instead.

Also update the write functions to cache the spec by default.

How to test the behavior?

Show how to reproduce the new behavior (can be a bug fix or a new feature)

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
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• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (dd6baaa) 91.99% compared to head (8bbe51a) 91.75%.

❗ Current head 8bbe51a differs from pull request most recent head 95717c6. Consider uploading reports for the commit 95717c6 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1782      +/-   ##
==========================================
- Coverage   91.99%   91.75%   -0.25%     
==========================================
  Files          27       27              
  Lines        2623     2619       -4     
  Branches      685      684       -1     
==========================================
- Hits         2413     2403      -10     
- Misses        138      141       +3     
- Partials       72       75       +3     

Flag	Coverage Δ
integration	71.09% <ø> (+0.07%)	⬆️
unit	84.38% <ø> (+0.70%)	⬆️

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