Do not auto-set timezone, allow date

[rly]

Motivation

Fix #1859, fix #1843

1. Date strings (e.g., "2024-04-10" without the "T") can now be roundtripped, so if a user writes a datetime.date object, it will be written without the "T" and read as a datetime.date object.
2. The local timezone is no longer automatically set on a non-timezone-aware datetime
3. timestamps_reference_time is allowed to be timezone-naive
4. Subject date_of_birth, file session_start_time, file file_create_date, and file timestamps_reference_time now allow date in addition to datetime

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.01%. Comparing base (001a9fd) to head (10060e6).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1886      +/-   ##
==========================================
+ Coverage   91.81%   92.01%   +0.20%     
==========================================
  Files          27       27              
  Lines        2627     2619       -8     
  Branches      688      685       -3     
==========================================
- Hits         2412     2410       -2     
+ Misses        142      139       -3     
+ Partials       73       70       -3     

Flag	Coverage Δ
integration	72.81% <100.00%> (+0.33%)	⬆️
unit	83.92% <77.77%> (+0.10%)	⬆️

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[rly]

@bendichter What do you think about this approach?

[bendichter]

Looks great!!! Do we still have tests that include timezones? (I'm on my phone)

[rly]

Great, thanks. I removed the affected tests and added some tests to ensure that the following cases work:

1. datetime with time zone
2. datetime without time zone
3. date

I want to add a few more tests and remove timezone from a few tests, so this is not ready to merge yet.

[bendichter]

ok. Looks great so far!

[rly]

I think given a dataset spec or attribute spec with dtype isodatetime, the mapping of a string value to a datetime or date object should occur in HDMF on construction of the object, rather than as a custom constructor argument override on every field that we know has an isodatetime spec. Requiring the override to get the string as a datetime or date object creates a burden on any extension that wants to store datetimes and read datetime data as datetime objects instead of as strings.

So, parse_datetime should move to HDMF's ObjectMapper. I'll create an issue on HDMF. If it takes longer to implement that than the next pynwb release, we can just merge this change and remove it later once HDMF handles the mapping.