Declare input and output types of commands (#6796)

* Add failing test that list of ints and floats is List<Number>

* Start defining subtype relation

* Make it possible to declare input and output types for commands

- Enforce them in tests

* Declare input and output types of commands

* Add formatted signatures to `help commands` table

* Revert SyntaxShape::Table -> Type::Table change

* Revert unnecessary derive(Hash) on SyntaxShape

Co-authored-by: JT <547158+jntrnr@users.noreply.github.com>

crates/nu-command/src/strings/str_/trim/trim_.rs

@@ -4,7 +4,7 @@ use nu_engine::CallExt;
 use nu_protocol::{
     ast::{Call, CellPath},
     engine::{Command, EngineState, Stack},
-    Example, PipelineData, ShellError, Signature, Span, Spanned, SyntaxShape, Value,
+    Example, PipelineData, ShellError, Signature, Span, Spanned, SyntaxShape, Type, Value,
 };
 
 #[derive(Clone)]
@@ -39,7 +39,9 @@ impl Command for SubCommand {
 
     fn signature(&self) -> Signature {
         Signature::build("str trim")
-            .rest(
+        .input_output_types(vec![(Type::String, Type::String)])
+        .vectorizes_over_list(true)
+        .rest(
                 "rest",
                 SyntaxShape::CellPath,
                 "optionally trim text by column paths",