Fix to_timedelta_int comment to accurately describe banker's rounding

[Copilot]

The comment on to_timedelta_int claimed it rounds "to the nearest whole ms," which is misleading — Python's round() uses banker's rounding (round-half-to-even), not conventional 0.5-up rounding.

Changes

• scripts/codegen/python.ts / python/copilot/generated/session_events.py: Replace assert milliseconds.is_integer() + int() cast with round(), and update the comment to explicitly note banker's rounding semantics:

def to_timedelta_int(x: timedelta) -> int:
    assert isinstance(x, timedelta)
    milliseconds = x.total_seconds() * 1000.0
    # Durations can carry sub-millisecond precision; round to the nearest whole ms
    # using Python's default banker's rounding (round-half-to-even).
    return round(milliseconds)