Warn if writing a file without the appropriate extension

[stephprince]

Motivation

Fix #1976 for NWBHDF5IO.

How to test the behavior?

from datetime import datetime
from dateutil.tz import tzutc
from pynwb import NWBFile, NWBHDF5IO

nwbfile = NWBFile(session_description='a test NWB File',
                             identifier='TEST123',
                             session_start_time=datetime(1970, 1, 1, 12, tzinfo=tzutc()))
with NWBHDF5IO("path.h5", 'w') as io:
    io.write(nwbfile)

Warns:

UserWarning: The file path provided: path.h5 does not end in '.nwb'. It is recommended that NWB files using the HDF5 backend use the '.nwb' extension

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?
• Is your contribution compliant with our coding style? This can be checked running ruff check . && codespell from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• 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 ✅

Project coverage is 91.87%. Comparing base (2f2a494) to head (0f1de82).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1978   +/-   ##
=======================================
  Coverage   91.87%   91.87%           
=======================================
  Files          27       27           
  Lines        2695     2697    +2     
  Branches      703      704    +1     
=======================================
+ Hits         2476     2478    +2     
  Misses        145      145           
  Partials       74       74           

Flag	Coverage Δ
integration	72.71% <100.00%> (+0.02%)	⬆️
unit	83.27% <0.00%> (-0.07%)	⬇️

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