Added custom validator for Resource mime type which is less retrictiv…

[sighthon]

Implemented RFC 2045-compliant MIME validation using the email.message parser to ensure correct type/subtype structure. The update adds strict checks for mandatory components but relaxed check for parameter keys and values.

Fixes #1756

How Has This Been Tested?

Exhautive tests covering varied mime_types have been added.

Breaking Changes

N/A

Types of changes

• [X ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• [X ] I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• [X ] I have added appropriate error handling
• [ X] I have added or updated documentation as needed

Additional context

https://www.iana.org/assignments/media-types/media-types.xhtml