Introduce new command - nu check (#5864)

* nu check command - 1

* Support stream

* Polish code and fix corner case

crates/nu-command/src/system/mod.rs

@@ -1,6 +1,7 @@
 mod benchmark;
 mod complete;
 mod exec;
+mod nu_check;
 mod ps;
 mod run_external;
 mod sys;
@@ -9,6 +10,7 @@ mod which_;
 pub use benchmark::Benchmark;
 pub use complete::Complete;
 pub use exec::Exec;
+pub use nu_check::NuCheck;
 pub use ps::Ps;
 pub use run_external::{External, ExternalCommand};
 pub use sys::Sys;