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/system/nu_check.rs

@@ -1,4 +1,4 @@
-use nu_engine::{command_prelude::*, env::get_config, find_in_dirs_env, get_dirs_var_from_call};
+use nu_engine::{command_prelude::*, find_in_dirs_env, get_dirs_var_from_call};
 use nu_parser::{parse, parse_module_block, parse_module_file_or_dir, unescape_unquote_string};
 use nu_protocol::engine::{FileStack, StateWorkingSet};
 use std::path::Path;
@@ -59,7 +59,7 @@ impl Command for NuCheck {
                 }
             }
             PipelineData::ListStream(stream, ..) => {
-                let config = get_config(engine_state, stack);
+                let config = stack.get_config(engine_state);
                 let list_stream = stream.into_string("\n", &config);
                 let contents = Vec::from(list_stream);
 

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

@@ -366,7 +366,7 @@ pub fn command_not_found(
     stack: &mut Stack,
 ) -> ShellError {
     // Run the `command_not_found` hook if there is one.
-    if let Some(hook) = &engine_state.config.hooks.command_not_found {
+    if let Some(hook) = &stack.get_config(engine_state).hooks.command_not_found {
         let mut stack = stack.start_capture();
         // Set a special environment variable to avoid infinite loops when the
         // `command_not_found` hook triggers itself.