refactor(nush): remove mutable variables from nushell init script

mutable variables, while supported, are considered unwanted in nu

Author: pheenty

src/shell/scripts/omp.nu

@@ -31,27 +31,23 @@ def --wrapped _omp_get_prompt [
     type: string,
     ...args: string
 ] {
-    mut execution_time = -1
-    mut no_status = true
     # We have to do this because the initial value of `$env.CMD_DURATION_MS` is always `0823`, which is an official setting.
     # See https://github.com/nushell/nushell/discussions/6402#discussioncomment-3466687.
-    if $env.CMD_DURATION_MS != '0823' {
-        $execution_time = $env.CMD_DURATION_MS | into int
-        $no_status = false
+    let execution_time = match $env.CMD_DURATION_MS {
+        '0823' => -1
+        $ms => { $ms | into int }
     }
 
-    (
-        ^$_omp_executable print $type
-            --save-cache
-            --shell=nu
-            $"--shell-version=($env.POSH_SHELL_VERSION)"
-            $"--status=($env.LAST_EXIT_CODE)"
-            $"--no-status=($no_status)"
-            $"--execution-time=($execution_time)"
-            $"--terminal-width=((term size).columns)"
-            $"--job-count=(job list | length)"
-            ...$args
-    )
+    ^$_omp_executable print $type
+        --save-cache
+        --shell=nu
+        $"--shell-version=($env.POSH_SHELL_VERSION)"
+        $"--status=($env.LAST_EXIT_CODE)"
+        $"--no-status=($execution_time < 0)"
+        $"--execution-time=($execution_time)"
+        $"--terminal-width=((term size).columns)"
+        $"--job-count=(job list | length)"
+        ...$args
 }
 
 $env.PROMPT_MULTILINE_INDICATOR = (
@@ -63,10 +59,10 @@ $env.PROMPT_MULTILINE_INDICATOR = (
 $env.PROMPT_COMMAND = {||
     # hack to set the cursor line to 1 when the user clears the screen
     # this obviously isn't bulletproof, but it's a start
-    mut clear = false
-    if $nu.history-enabled {
-        $clear = (history | is-empty) or ((history | last 1 | get 0.command) == "clear")
-    }
+    let clear = $nu.history-enabled and (
+        (history | is-empty)
+        or (history | last | get command?) == "clear"
+    )
 
     if ($env.SET_POSHCONTEXT? | is-not-empty) {
         do --env $env.SET_POSHCONTEXT