Update config directly at assignment (#13332)

# Description

Allows `Stack` to have a modified local `Config`, which is updated
immediately when `$env.config` is assigned to. This means that even
within a script, commands that come after `$env.config` changes will
always see those changes in `Stack::get_config()`.

Also fixed a lot of cases where `engine_state.get_config()` was used
even when `Stack` was available.

Closes #13324.

# User-Facing Changes
- Config changes apply immediately after the assignment is executed,
rather than whenever config is read by a command that needs it.
- Potentially slower performance when executing a lot of lines that
change `$env.config` one after another. Recommended to get `$env.config`
into a `mut` variable first and do modifications, then assign it back.
- Much faster performance when executing a script that made
modifications to `$env.config`, as the changes are only parsed once.

# Tests + Formatting
All passing.

# After Submitting
- [ ] release notes

crates/nu-command/src/formats/to/md.rs

@@ -70,8 +70,8 @@ impl Command for ToMd {
         let head = call.head;
         let pretty = call.has_flag(engine_state, stack, "pretty")?;
         let per_element = call.has_flag(engine_state, stack, "per-element")?;
-        let config = engine_state.get_config();
-        to_md(input, pretty, per_element, config, head)
+        let config = stack.get_config(engine_state);
+        to_md(input, pretty, per_element, &config, head)
     }
 }
 

crates/nu-command/src/formats/to/text.rs

@@ -31,18 +31,19 @@ impl Command for ToText {
     fn run(
         &self,
         engine_state: &EngineState,
-        _stack: &mut Stack,
+        stack: &mut Stack,
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         let span = call.head;
         let input = input.try_expand_range()?;
+        let config = stack.get_config(engine_state);
 
         match input {
             PipelineData::Empty => Ok(Value::string(String::new(), span)
                 .into_pipeline_data_with_metadata(update_metadata(None))),
             PipelineData::Value(value, ..) => {
-                let str = local_into_string(value, LINE_ENDING, engine_state.get_config());
+                let str = local_into_string(value, LINE_ENDING, &config);
                 Ok(
                     Value::string(str, span)
                         .into_pipeline_data_with_metadata(update_metadata(None)),
@@ -50,7 +51,6 @@ impl Command for ToText {
             }
             PipelineData::ListStream(stream, meta) => {
                 let span = stream.span();
-                let config = engine_state.get_config().clone();
                 let iter = stream.into_inner().map(move |value| {
                     let mut str = local_into_string(value, LINE_ENDING, &config);
                     str.push_str(LINE_ENDING);