Add level and msg type hints to MultiProcessAdapter.log

[RudrenduPaul]

What this PR does

Adds type hints to the level and msg parameters of
MultiProcessAdapter.log() in src/accelerate/logging.py:

def log(self, level: int, msg: object, *args, **kwargs):

MultiProcessAdapter subclasses logging.LoggerAdapter, and this matches
the standard library's own typeshed signature for
LoggerAdapter.log(self, level: int, msg: object, ...) — level is always
an integer logging level (e.g. logging.INFO), and msg is typed as
object rather than str because Python's logging module accepts any
object with a __str__ (including lazy-formatting helper objects), and
that's exactly how this method is exercised elsewhere via
self.isEnabledFor(level) and self.process(msg, kwargs).

This is a self-identified typing-consistency follow-up (no linked issue) —
a small companion to my other open PR (#4123, type hints in
utils/imports.py), which touches a different file in the same repo.

No behaviour change

Type-hint-only change. No logic was modified. The file already has
from __future__ import annotations at the top, so this adds no runtime
overhead.

Testing

• ruff check src/accelerate/logging.py — 1 pre-existing finding
  (unrelated functools.lru_cache on warning_once), not on the changed
  line, not introduced by this change (verified against upstream main
  before/after via git stash).
• ruff format --diff src/accelerate/logging.py — no diff, file already
  formatted.

Note: Claude Code was used to assist in drafting this change. All
changes were reviewed by the submitter.