completion_refresh thread crashes with KeyError

[shgol]

Description

I get the following Exception a few seconds after connecting to the db

Traceback (most recent call last):
  File "/opt/homebrew/Cellar/python@3.14/3.14.4_1/Frameworks/Python.framework/Versions/3.14/lib/python3.14/threading.py", line 1082, in _bootstrap_inner
    self._context.run(self.run)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.14/3.14.4_1/Frameworks/Python.framework/Versions/3.14/lib/python3.14/threading.py", line 1024, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/pgcli/4.4.0_1/libexec/lib/python3.14/site-packages/pgcli/completion_refresher.py", line 63, in _bg_refresh
    refresher(completer, executor)
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/pgcli/4.4.0_1/libexec/lib/python3.14/site-packages/pgcli/completion_refresher.py", line 111, in refresh_tables
    completer.extend_columns(executor.table_columns(), kind="tables")
    ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/pgcli/4.4.0_1/libexec/lib/python3.14/site-packages/pgcli/pgcompleter.py", line 232, in extend_columns
    metadata[schema][relname][colname] = column
    ~~~~~~~~~~~~~~~~^^^^^^^^^
KeyError: 'some_table_name'

You can reproduce this by creating a table in between the calls to extend_relations and extend_columns in completion_refresher.py. The dict keyed on relname doesn't get created, and then after the table is created extend_columns looks up the new table and gets KeyError.
I repro this consistently due to another process programmatically creating tables often.

repro'd on pgcli 4.4.0