Pydantic error messages for problems in config-g2p files are unfriendly

[joanise]

Before the conversion to Pydantic, problems in the config files would raise MalformedMapping with an (at least somewhat) informative message.

Now we get a pydantic error that's much harder to interpret. We should try to catch it it the right place and augment it with user-informative details.

E.g., set abbreviations_path: 1.0 in any mapping config and running g2p udpate yields this:

$ g2p update
INFO - Loading alignments from c:\users\joanise\sandboxes\g2p\g2p\mappings\langs\eng\cmudict.ipa.aligned.txt
Traceback (most recent call last):
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\Scripts\g2p-script.py", line 33, in <module>
    sys.exit(load_entry_point('g2p', 'console_scripts', 'g2p')())
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 1128, in __call__
    return self.main(*args, **kwargs)
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 1053, in main
    rv = self.invoke(ctx)
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 1659, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 1395, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 754, in invoke
    return __callback(*args, **kwargs)
  File "c:\users\joanise\sandboxes\g2p\g2p\cli.py", line 662, in update
    cache_langs(dir_path=in_dir, langs_path=langs_path, network_path=network_path)
  File "c:\users\joanise\sandboxes\g2p\g2p\mappings\langs\utils.py", line 163, in cache_langs
    mapping_config = MappingConfig.load_mapping_config_from_path(path)
  File "c:\users\joanise\sandboxes\g2p\g2p\mappings\__init__.py", line 434, in load_mapping_config_from_path
    return MappingConfig(**loaded_config)
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\pydantic\main.py", line 171, in __init__
    self.__pydantic_validator__.validate_python(data, self_instance=self)
pydantic_core._pydantic_core.ValidationError: 1 validation error for MappingConfig
mappings.0.abbreviations_path
  Input is not a valid path [type=path_type, input_value=1.0, input_type=float]

Or, a more realistic case where the file just doesn't exist:

$ g2p update
INFO - Loading alignments from c:\users\joanise\sandboxes\g2p\g2p\mappings\langs\eng\cmudict.ipa.aligned.txt
Traceback (most recent call last):
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\Scripts\g2p-script.py", line 33, in <module>
    sys.exit(load_entry_point('g2p', 'console_scripts', 'g2p')())
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 1128, in __call__
    return self.main(*args, **kwargs)
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 1053, in main    
    rv = self.invoke(ctx)
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 1659, in invoke  
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 1395, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\click\core.py", line 754, in invoke
    return __callback(*args, **kwargs)
  File "c:\users\joanise\sandboxes\g2p\g2p\cli.py", line 662, in update
    cache_langs(dir_path=in_dir, langs_path=langs_path, network_path=network_path)
  File "c:\users\joanise\sandboxes\g2p\g2p\mappings\langs\utils.py", line 163, in cache_langs
    mapping_config = MappingConfig.load_mapping_config_from_path(path)
  File "c:\users\joanise\sandboxes\g2p\g2p\mappings\__init__.py", line 434, in load_mapping_config_from_path
    return MappingConfig(**loaded_config)
  File "C:\Users\joanise\Miniconda3\envs\ras-py310\lib\site-packages\pydantic\main.py", line 171, in __init__
    self.__pydantic_validator__.validate_python(data, self_instance=self)
  File "c:\users\joanise\sandboxes\g2p\g2p\mappings\__init__.py", line 51, in model_post_init
    self.abbreviations = load_abbreviations_from_file(
  File "c:\users\joanise\sandboxes\g2p\g2p\mappings\utils.py", line 426, in load_abbreviations_from_file
    with open(path, encoding="utf8") as f:
FileNotFoundError: [Errno 2] No such file or directory: 'c:\\users\\joanise\\sandboxes\\g2p\\g2p\\mappings\\langs\\fra\\file_does_not_exist.csv'

The stack trace is not really helpful, and there is no indicate as to which config file has the problem, which is what the user needs to know.