pool: Handle non-shard-aware endpoints in logging

[tchaikov]

When connecting to non-shard-aware endpoints, conn.features.shard_id is None. Previously, this would cause a TypeError when logging with %i format specifier.

  Traceback (most recent call last):
    File "/usr/lib64/python3.12/logging/__init__.py", line 1160, in emit
      msg = self.format(record)
            ^^^^^^^^^^^^^^^^^^^
    File "/usr/lib64/python3.12/logging/__init__.py", line 999, in format
      return fmt.format(record)
             ^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3.12/site-packages/_pytest/logging.py", line 136, in format
      return super().format(record)
             ^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/lib64/python3.12/logging/__init__.py", line 703, in format
      record.message = record.getMessage()
                       ^^^^^^^^^^^^^^^^^^^
    File "/usr/lib64/python3.12/logging/__init__.py", line 392, in getMessage
      msg = msg % self.args
            ~~~~^~~~~~~~~~~
  TypeError: %i format: a real number is required, not NoneType
  Call stack:
    File "/usr/lib64/python3.12/threading.py", line 1032, in _bootstrap
      self._bootstrap_inner()
    File "/usr/lib64/python3.12/threading.py", line 1075, in _bootstrap_inner
      self.run()
    File "/usr/lib64/python3.12/threading.py", line 1012, in run
      self._target(*self._args, **self._kwargs)
    File "/usr/lib64/python3.12/concurrent/futures/thread.py", line 92, in _worker
      work_item.run()
    File "/usr/lib64/python3.12/concurrent/futures/thread.py", line 58, in run
      result = self.fn(*self.args, **self.kwargs)
  Message: 'Received a connection %s for shard_id=%i on host %s'
  Arguments: (140333813254336, None, <Host: 127.67.173.34:9042 dc2>)

Now prints -1 as a fallback value instead of raising an exception.

This fixes logging failures that occurred when:

• Connecting to non-shard-aware endpoints
• Debug logging level was enabled

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• I added relevant tests for new features and bug fixes.
• All commits compile, pass static checks and pass test.
• PR description sums up the changes and reasons why they should be introduced.
• I have provided docstrings for the public items that I want to introduce.
• I have adjusted the documentation in ./docs/source/.
• I added appropriate Fixes: annotations to PR description.

[tchaikov]

see https://jenkins.scylladb.com/job/scylla-master/job/scylla-ci/14179/consoleFull for an example of the error addressed by this change.