Only run $env.PROMPT_COMMAND once per prompt (copy of #10986) (#11366)

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# Description
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This PR is basically a copy of #10986 by @CAD97, which made
`$env.PROMPT_COMMAND` only run once per prompt, but @fdncred found an
issue where hitting Enter would make the transient prompt appear and be
immediately overwritten by the regular prompt, so it was
[reverted](https://github.com/nushell/nushell/pull/11340).
https://github.com/nushell/nushell/pull/10788 was also made to do the
same thing as #10986 but that ended up having the same issue. For some
reason, this branch doesn't have that problem, although I haven't
figured out why yet.

@CAD97, if you have any inputs or want to make your own PR, let me know.

# User-Facing Changes
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When hitting enter, the prompt shouldn't blink in place anymore.

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crates/nu-cli/src/repl.rs

@@ -29,7 +29,7 @@ use std::{
     env::temp_dir,
     io::{self, IsTerminal, Write},
     path::Path,
-    sync::{atomic::Ordering, Arc, RwLock},
+    sync::atomic::Ordering,
     time::Instant,
 };
 use sysinfo::SystemExt;
@@ -69,7 +69,7 @@ pub fn evaluate_repl(
 
     let mut entry_num = 0;
 
-    let nu_prompt = Arc::new(RwLock::new(NushellPrompt::new(config.shell_integration)));
+    let mut nu_prompt = NushellPrompt::new(config.shell_integration);
 
     let start_time = std::time::Instant::now();
     // Translate environment variables from Strings to Values
@@ -268,12 +268,7 @@ pub fn evaluate_repl(
             .with_quick_completions(config.quick_completions)
             .with_partial_completions(config.partial_completions)
             .with_ansi_colors(config.use_ansi_coloring)
-            .with_cursor_config(cursor_config)
-            .with_transient_prompt(prompt_update::transient_prompt(
-                Arc::clone(&nu_prompt),
-                engine_reference.clone(),
-                stack,
-            ));
+            .with_cursor_config(cursor_config);
         perf(
             "reedline builder",
             start_time,
@@ -426,7 +421,9 @@ pub fn evaluate_repl(
 
         start_time = std::time::Instant::now();
         let config = &engine_state.get_config().clone();
-        prompt_update::update_prompt(config, engine_state, stack, Arc::clone(&nu_prompt));
+        prompt_update::update_prompt(config, engine_state, stack, &mut nu_prompt);
+        let transient_prompt =
+            prompt_update::make_transient_prompt(config, engine_state, stack, &nu_prompt);
         perf(
             "update_prompt",
             start_time,
@@ -439,14 +436,8 @@ pub fn evaluate_repl(
         entry_num += 1;
 
         start_time = std::time::Instant::now();
-        let input = {
-            line_editor.read_line(
-                &nu_prompt
-                    .read()
-                    .expect("Could not lock on prompt to pass to read_line")
-                    .to_owned(),
-            )
-        };
+        line_editor = line_editor.with_transient_prompt(transient_prompt);
+        let input = line_editor.read_line(&nu_prompt);
         let shell_integration = config.shell_integration;
 
         match input {