fix: Catch multiple leak occurrences in same string

[diogosilva30]

Main change

• Allows to catch more than 1 leak in same string. Before only the first instance was being catch, and tests were also looking at this case. Tests were updated to cover these more complex cases.

Example:

from maskerlogger import mask_string
my_str="This is some confidential line, and the user password: mysuperSecretPassword and btw the user apiKey=AIzaSyabcdefghijklmnopqrstuvwxyz1234567"
# Output:
# This is some confidential line, and the user password: ********************* and btw the user apiKey=***************************************
# Before this change only the password would have been masked and not the ApiKey :(

• Removes the main masking logic from AbstractMaskedLogger and instead logic is placed into a independent function mask_string. This allow + flexible usage of the codebase. For example, in my use case I want to have access to this function to cleanup a string outside of logging context, but since logic is currently hidden inside AbstractMaskedLogger._mask_sensitive_data and the argument is a LogRecord we cannot use this logic for more generic cases. By abstracting away the logic to an independent mask_string method we can use this code base into other use-cases. Retro-compatibility is ensured by calling mask_string inside AbstractMaskedLogger._mask_sensitive_data.

Example use case:

from maskerlogger import mask_string
my_str= "Here I have a generic string with a potential leak. Password: mypasswordoops"
masked_my_str=mask_string(my_str)
# Done! My str was cleaned into a context that is not related to logging at all. Awesome library :) 

Additional

• Performs general code cleanup (more pythonic code, better type hints, code formatting, etc)
• Changes the rule generic-api-key to allow common chars that are used in passwords/api keys, and reduce minimum length to 8 instead of 10, as it's very common for passwords to have 8 as required minimum chars

[diogosilva30]

@nvuillam @tamar-ox @oxnick Please let me know if you find these changes useful and if something should be changed