Fix Issue #1017 and refactoring Mapster.Tool for ease of testing - #1019

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-dotnet@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Converting null literal or possible null value to non-nullable type.

Possible null reference return.

Converting null literal or possible null value to non-nullable type.

Possible null reference return.

Converting null literal or possible null value to non-nullable type.

Non-nullable property 'Name' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Type' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Nullability of type of parameter 'obj' doesn't match overridden member (possibly because of nullability attributes).

Possible null reference return.