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/stor/insert.rs

@@ -65,7 +65,7 @@ impl Command for StorInsert {
         let span = call.head;
         let table_name: Option<String> = call.get_flag(engine_state, stack, "table-name")?;
         let data_record: Option<Record> = call.get_flag(engine_state, stack, "data-record")?;
-        // let config = engine_state.get_config();
+        // let config = stack.get_config(engine_state);
         let db = Box::new(SQLiteDatabase::new(
             std::path::Path::new(MEMORY_DB),
             Signals::empty(),