Interactive problems via IO

[DietPawel]

We have a request to support interactive problems via stdio + flush rather than with a library on Szkopuł.

Consider this as an example

[MasloMaslane]

Interactive tasks with IO described by Krzysztof Małysa in his master thesis in point 4.14.1: https://github.com/varqox/masters_thesis/blob/main/main.pdf

Source code for interactive tasks with IO: https://github.com/varqox/sim-project/blob/main/subprojects/simlib/src/sim/judge/test_on_interactive_test.cc

Unit tests: https://github.com/varqox/sim-project/blob/main/subprojects/simlib/test/sim/judge/test_on_interactive_test.cc

[DietPawel]

I think we can get away without introducing third process to forward the communication as described in the 4.14.1 by utilizing WTERMSIG on status from waitpid(2). If the user process returns due to SIGPIPE we can ignore it if checker gave us the answer or treat it as SE when checker did not gave the verdict.

[geoff128]

https://docs.google.com/document/d/1UEEOPyCRUpJRQv_nfrapkYvn31wIE604Z6beHlZPiW8/edit?usp=sharing