fix(ws): replace deprecated utcfromtimestamp in vendored well_known_types

[roson9527]

Summary

Fixes #145.

The bundled protobuf stub at lark_oapi/ws/pb/google/protobuf/internal/well_known_types.py still calls datetime.datetime.utcfromtimestamp(0), which is deprecated in Python 3.12+ and emits DeprecationWarning on Python 3.13/3.14. This breaks test runs that elevate DeprecationWarning to errors and will turn into a hard failure once Python removes the API.

Change

Align with current upstream protocolbuffers/protobuf (python/google/protobuf/internal/well_known_types.py) by constructing the epoch datetime directly instead of via the deprecated helper:

# before
_EPOCH_DATETIME_NAIVE = datetime.datetime.utcfromtimestamp(0)
_EPOCH_DATETIME_AWARE = datetime.datetime.fromtimestamp(0, tz=datetime.timezone.utc)

# after
_EPOCH_DATETIME_NAIVE = datetime.datetime(1970, 1, 1, tzinfo=None)
_EPOCH_DATETIME_AWARE = _EPOCH_DATETIME_NAIVE.replace(tzinfo=datetime.timezone.utc)

Semantics preserved: _EPOCH_DATETIME_NAIVE stays a naive UTC datetime, _EPOCH_DATETIME_AWARE stays timezone-aware UTC. Callers at lines 251/266 (_EPOCH_DATETIME_NAIVE + delta / _EPOCH_DATETIME_AWARE + delta) are unchanged.

Verification

• Python 3.14.6: importing the module with warnings.simplefilter('error', DeprecationWarning) no longer raises.
• Confirmed _EPOCH_DATETIME_NAIVE == datetime(1970, 1, 1) and _EPOCH_DATETIME_AWARE == datetime(1970, 1, 1, tzinfo=timezone.utc), matching pre-change values.
• rg "utcfromtimestamp" lark_oapi/ returns no matches.

Scope

Single-file, 3-line change to vendored protobuf code. No API change, no dependency change.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

roson seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}