fix: handle 7-digit fractional seconds in _parse_iso for Python 3.10

Python 3.10's fromisoformat only supports up to 6 fractional digits
(microseconds). Teams sends 7-digit timestamps (e.g., .4513813).
Truncate extra digits before parsing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: patrick-chinchill

src/chat_sdk/types.py

@@ -24,9 +24,17 @@
 def _parse_iso(s: str) -> datetime:
     """Parse ISO 8601 datetime string, supporting Python 3.10+.
 
-    Python 3.10's ``fromisoformat`` doesn't accept the ``Z`` suffix.
+    Handles two Python 3.10 limitations:
+    - ``Z`` suffix not accepted (replaced with ``+00:00``)
+    - Fractional seconds limited to 6 digits (truncated from 7+)
     """
-    return datetime.fromisoformat(s.replace("Z", "+00:00"))
+    import re
+
+    s = s.replace("Z", "+00:00")
+    # Python 3.10 only supports up to 6 fractional digits (microseconds).
+    # Truncate any extra digits (e.g., Teams sends 7-digit nanosecond timestamps).
+    s = re.sub(r"(\.\d{6})\d+", r"\1", s)
+    return datetime.fromisoformat(s)
 
 
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