Change epoch tags to property

[stephprince]

Motivation

• Fix [Bug]: epoch_tags not written to disk #1901.
• Fix [Bug]: EpochTags #1449.

epoch_tags could be assigned in the NWBFile constructor, but it was never written to disk. It could also be out of sync with the epochs table. It seems that it was maybe originally meant to be a shortcut for getting all of the unique epoch tags from the epochs table.

As a side effect of this change, epoch_tags would no longer be displayed by __repr__ or _repr_html_ (I looked a little into getting it to display, but if we include properties in the reprs it makes several other different datatype print outs less clean).

See related discussion about deprecating here: #1521 (comment)

How to test the behavior?

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

nwbfile = NWBFile(
    session_id='test',
    session_description='test',
    identifier='12345',
    session_start_time=(
        datetime.now(tzlocal())
    ),
)
nwbfile.add_epoch(start_time=1.0, stop_time=10.0, tags=["tag1", "tag2"])
nwbfile.add_epoch(start_time=10.0, stop_time=20.0, tags=["tag1", "tag3"])
nwbfile.add_epoch(start_time=1.0, stop_time=10.0, tags="tag4")
print(f'memory: {nwbfile.epoch_tags}').  # memory: {'tag3', 'tag1', 'tag4', 'tag2'}

path = 'test1.nwb'
with NWBHDF5IO(path, 'w') as io:
    io.write(nwbfile)

with NWBHDF5IO(path, 'r') as io:
    nwb_read = io.read()
    print(f'disk: {nwb_read.epoch_tags}'). # disk: {'tag3', 'tag1', 'tag4', 'tag2'}

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 92.20%. Comparing base (a9f6332) to head (bc716a9).
Report is 16 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1935   +/-   ##
=======================================
  Coverage   92.20%   92.20%           
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  Files          27       27           
  Lines        2656     2656           
  Branches      693      693           
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  Hits         2449     2449           
  Misses        134      134           
  Partials       73       73           

Flag	Coverage Δ
integration	73.15% <66.66%> (ø)
unit	83.77% <100.00%> (ø)

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