[Feature]: Fix build warnings

[antoineatstariongroup]

What type of issue is this?

• Bug report
• Feature request

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of the SysML2.NET
• I have searched open and closed issues to ensure it has not already been reported

Description

The SysML2.NET.Serializer.Xmi project produce a lot of warning at build time. Those warning polluate github actions logs and lower the quality of the code.

Most of those warning comes from generated code, templates has to be fixed to remove those warning

Steps to Reproduce

System Configuration

• SysML2.NET version:
• Environment (Operating system, version and so on):
• .NET Framework version:
• Additional information: