CI refactoring

[kalaninja]

new workflow:

• linter. checks formatting. if ok then runs 2 next tasks in parallel
• check. does cargo check of trappist and stout to make sure that the code compiles
• test. runs cargo test --features runtime-benchmarks to execute all tests including benchmarks

github runners don't have limited space and memory. the following things were done to make tests runable:

• free disk space by removing unused components from Ubuntu image;
• keep check and test versions separately in cache;
• limit number of threads used by cargo. if a runner fails with error Process completed with exit code 143. number of threads might be reduced to 1;