avoid overwriting proofsEnabled through default parameter

[Trivo25]

MyProgram.setProofsEnabled(false);
await MyProgram.compile();

Wouldn't work because compile() sets the internal flag to true no matter what since that's the default parameter. The fix is to specify no default parameter (undefined by default) and only setting the internal flag if the developer actually passes in a value. This is backwards compatible because 1) the API doesn't change and 2) the internal flag is still initiated with true so its behavior stays the same

thanks for pointing this out @rpanic

[mitschabaude]

force merging as well because this now requires regression checks 1 and 2