Accept an ISO 8601 string as expiry_time in load_oauth_session

[Petru101]

Since the 0.9.0 changes, every request checks the access token's expiry time before it's sent (Requests._access_token_expired). Applications that pass expiry_time to load_oauth_session as a string, as they could until now because tidalapi never used it, now get AttributeError: 'str' object has no attribute 'tzinfo' on every request, including the sessions request inside load_oauth_session itself.

High Tide is one of them: it stores str(session.expiry_time) in the keyring and passes that back on the next start, so it would stop working with 0.9.0.

load_oauth_session now parses a string with datetime.fromisoformat, as load_session_from_file already does, and ignores it with a log message if it can't be parsed (e.g. "None"). The new offline tests in test_token_refresh.py cover str(datetime), an isoformat() string and an invalid string, and fail with that AttributeError without the change.

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[tehkillerbee]

Welcome and thanks for your contribution.

FYI I had a separate commit here that removes datetime.utcnow() usage (will be merged ASAP)
bee481b

This essentially means that we use timezone aware datetime, str() would return something like
2026-10-15 12:53:00.123456+00:00

So whether this works depends on how this string was generated. If it was generated using utcnow(), it should be treated as UTC. It will then look something like:
2026-10-15 12:53:00.123456

Something like this:

if isinstance(expiry_time, str):
    # Applications often store the expiry time as text
    try:
        expiry_time = datetime.datetime.fromisoformat(expiry_time)
    except ValueError:
        log.info("Ignoring invalid expiry_time %r", expiry_time)
        expiry_time = None

if expiry_time is not None and expiry_time.tzinfo is None:
    # Treat naive datetimes (e.g. from legacy utcnow()) as UTC
    expiry_time = expiry_time.replace(tzinfo=datetime.timezone.utc)