fix(provider): enhance error handling and type parsing in evaluations

[Abraxas-365]

1. Added handling for toggles where boolean values may be given as a string.
2. Added string parsing for float and integer evaluations, if the value given is a string.
3. Switched out static error messages for more dynamic and informative ones based on the flag type.
4. Enhanced user data extraction from the evaluation context and added user custom attributes.
5. Added helper functions to safely extract string values from maps and to determine if an attribute belongs to a user.