schwarz: semantics of problem classes

[Francesco Rizzi]

for the schwarz, we need to think whether we shold make a problem default constructible, assignable and movable, etc

i think: no default constructible, no copy assign, no move assign, but copy/move constrictible yes

see https://github.com/cwentland0/pressio-demoapps-schwarz/blob/main/include/pda-schwarz/schwarz.hpp