fix: update field naming to use snake_case in generated proto files

[ilCollez]

Fix: Use snake_case for proto field names

Problem

The types plugin was generating proto fields in camelCase (firstName, emailAddress) instead of the standard snake_case convention (first_name, email_address).

Solution

Changed types/proto.go line 169 to use codegen.SnakeCase() instead of codegen.Goify().

Testing

• Added TestProtoFieldNaming with tests for camelCase, acronyms, and multiple word fields
• All existing tests pass
• Verified with reproduction case showing correct conversions:
  • firstName => first_name
  • HTTPSEnabled => https_enabled
  • profilePictureURL => profile_picture_url