Formatting exception handling and fill_missing_fmt_key error

Start at fluent/handler.py around the linked line 151 and reproduce the Python 3.8+ formatting traceback. Trace how ValueError is handled for each style and how FluentRecordFormatter's fill_missing_fmt_key=True path responds; done means both formatting error handling and missing-key filling behave as intended.

There is ValueError is reraised instead of KeyError in the format method of each style class since python3.8:
https://github.com/python/cpython/issues/79025#issuecomment-1093800953

So formatting error handling and fill_missing_fmt_key=True arg of FluentRecordFormatter does not work correctly.

Traceback (most recent call last):
  File "/usr/lib/python3.10/logging/__init__.py", line 440, in format
    return self._format(record)
  File "/usr/lib/python3.10/logging/__init__.py", line 458, in _format
    return self._fmt.format(**values)
KeyError: 'kubernetes'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/django/core/management/base.py", line 330, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/django/core/management/commands/runserver.py", line 61, in execute
    super().execute(*args, **options)
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/django/core/management/base.py", line 371, in execute
    output = self.handle(*args, **options)
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/django/core/management/commands/runserver.py", line 96, in handle
    self.run(**options)
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/django/core/management/commands/runserver.py", line 103, in run
    autoreload.run_with_reloader(self.inner_run, **options)
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/django/utils/autoreload.py", line 617, in run_with_reloader
    logger.info('Watching for file changes with %s', reloader.__class__.__name__)
  File "/usr/lib/python3.10/logging/__init__.py", line 1477, in info
    self._log(INFO, msg, args, **kwargs)
  File "/usr/lib/python3.10/logging/__init__.py", line 1624, in _log
    self.handle(record)
  File "/usr/lib/python3.10/logging/__init__.py", line 1634, in handle
    self.callHandlers(record)
  File "/usr/lib/python3.10/logging/__init__.py", line 1696, in callHandlers
    hdlr.handle(record)
  File "/usr/lib/python3.10/logging/__init__.py", line 968, in handle
    self.emit(record)
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/fluent/handler.py", line 232, in emit
    data = self.format(record)
  File "/usr/lib/python3.10/logging/__init__.py", line 943, in format
    return fmt.format(record)
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/fluent/handler.py", line 97, in format
    data = self._formatter(record)
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/fluent/handler.py", line 154, in _format_by_dict
    raise exc
  File "/home/nz/.local/lib/virtualenvs/platform10/lib/python3.10/site-packages/fluent/handler.py", line 148, in _format_by_dict
    value = self.__style(value).format(record)
  File "/usr/lib/python3.10/logging/__init__.py", line 442, in format
    raise ValueError('Formatting field not found in record: %s' % e)
ValueError: Formatting field not found in record: 'kubernetes'

ValueError must be handled here