Support custom namespaces for dg_ctl create model(#1591)

[two-headBoy]

Description

This PR resolves feature request #1591, decoupling generated model namespace from raw database name and providing two ways to customize namespace: command line argument --namespace and namespace field in model.json.

Changes

1. Command Entry & Header Definition

• drogon_ctl/create.cc
  Update command help text to document --namespace option
• drogon_ctl/create_model.h
  Add namespaceName_ and namespaceOverridden_ member variables

2. Core Logic File

• drogon_ctl/create_model.cc
  • Add parsing logic for --namespace CLI argument
  • Read namespace value from model.json as fallback when no CLI override
  • Inject namespaceName_ into template render data for PG/MySQL/SQLite three database branches

3. Template Files (Dynamic Namespace Generation)

• drogon_ctl/templates/model_h.csp
  Dynamically generate namespace bracket blocks and closing comment
• drogon_ctl/templates/model_cc.csp
  Rewrite using namespace splicing logic to use custom namespace
• drogon_ctl/templates/restful_controller_base_h.csp
  Adapt using statement template
• drogon_ctl/templates/restful_controller_custom_h.csp
  Adapt using statement template

4. Test Script

• test.sh
  Add full SQLite test cases covering:
  • Config priority
  • CLI override
  • Empty namespace scenarios

Closes #1591

[an-tao]

@two-headBoy Thanks so much for your patch.