fix(postgresql): enforce public properties for PostgreSQL serialization

[maloun96]

Resolves PostgreSQL serialization issues caused by null bytes (\x00) in private/protected mailable properties. Adds configuration option enforce_public_properties to control property accessibility in mailable objects.

Changes:

• Add enforce_public_properties config option (default: false)
• Add constructor property validation to ensure compliance
• Add test coverage for property validation

[binaryk]

Thank you!