Fix: change auto-generated model fields prefix to suffix to avoid macros collisions

[afanofrafa]

Description of the problem I faced during the developing

Currently, drogon_ctl generates model field constants in the Cols struct with a leading underscore (e.g., _id, _name). This causes compilation issues on Windows (especially with MSVC) due to collisions with system macros and standard library reserved identifiers.

This PR moves the underscore to the end of the variable name (e.g., id_, name_) in the generated templates to follow standard C++ naming conventions and avoid these collisions.

Changes made

• Updated drogon_ctl/templates/model_h.csp and drogon_ctl/templates/model_cc.csp templates.
• Changed the generated field names in the Cols struct from _fieldName to fieldName_.

Note: This is a breaking change for existing user code that directly uses ModelName::Cols::_fieldName in their ORM queries, but it is necessary for cross-platform compatibility.