change _create_modelsim_ini() and add ini_flag="ini" for questsim>=ve…

[asicnet]

In File modelsim.py method _create_modelsim_ini

Many problems arise when libraries already exist or when certain files—usually protected—need to be precompiled. This can be solved with env. VUNIT_MODELSIM_INI, but not if modelsim.ini changes after vunit compile or even during it. The initial modelsim.ini must first be adjusted again because vunit creates a new modelsim each time. This is a hindrance for very complex designs. Therefore, the suggestion is NOT to overwrite modelsim.ini if it already exists.

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Questasim change the option for modelsim.ini from -modelsimini to -ini. So add a member ini_flag and change all -modelsimini to f"{self.ini_flag} and add a version check if vsim < 2025 for modelsimini