Introduce use of app-specific exceptions

[mrchrisadams]

This pull request includes several changes to improve error handling and logging in the carbon_txt CLI application. The most important changes involve replacing sys.exit calls with typer.Exit for better integration with Typer, enhancing exception handling, and adding new tests for missing files.

Error Handling Improvements:

• Replaced sys.exit calls with typer.Exit in various functions for better integration with Typer. [1] [2] [3] [4] [5] [6]
• Enhanced exception handling in validate_file to catch specific exceptions (FileNotFoundError, UnreachableCarbonTxtFile, NotParseableTOML) and log appropriate messages.

Logging Enhancements:

• Added logging statements in validate_file to log the discovery and parsing of carbon.txt files.

Exception Handling Enhancements:

• Introduced new exceptions (UnreachableCarbonTxtFile, NotParseableTOML) in exceptions.py to handle specific error cases.
• Updated finders.py and parsers_toml.py to use the new exceptions for better error reporting. [1] [2] [3] [4]

Testing Improvements:

• Added a new test in test_cli.py to check the behavior when a carbon.txt file is missing.