custom-completions: scoop: improve performance of getting scoop commands (#988)

Instead of calling scoop that calls powershell, use nushell's native
commands.

On Windows 11 virtual machine,
powershell takes `330ms 492µs 860ns` on **fastest** case,
with this commit takes `23ms 24µs 660ns` on **slowest**.

```nu
> use old-scoop-completions.nu *
> let oldTimes = (1..10 | each { timeit { scoopCommands } })
> $oldTimes | sort --reverse
╭───┬───────────────────╮
│ 0 │ 357ms 565µs 720ns │
│ 1 │  344ms 64µs 450ns │
│ 2 │ 343ms 264µs 680ns │
│ 3 │  342ms 686µs 10ns │
│ 4 │ 342ms 241µs 740ns │
│ 5 │ 338ms 365µs 910ns │
│ 6 │ 337ms 682µs 790ns │
│ 7 │ 335ms 473µs 290ns │
│ 8 │ 335ms 186µs 830ns │
│ 9 │ 330ms 492µs 860ns │
╰───┴───────────────────╯
> $oldTimes | math avg
340ms 702µs 428ns

> use scoop-completions.nu *
> let newTimes = (1..10 | each { timeit { scoopCommands } })
> $newTimes | sort --reverse
╭───┬──────────────────╮
│ 0 │  23ms 24µs 660ns │
│ 1 │  18ms 33µs 480ns │
│ 2 │ 15ms 597µs 650ns │
│ 3 │ 15ms 412µs 850ns │
│ 4 │  15ms 58µs 770ns │
│ 5 │  14ms 536µs 30ns │
│ 6 │  14ms 366µs 20ns │
│ 7 │ 14ms 175µs 270ns │
│ 8 │ 13ms 688µs 730ns │
│ 9 │ 13ms 378µs 590ns │
╰───┴──────────────────╯
> $newTimes | math avg
15ms 727µs 205ns
```

Author: e2dk4r

custom-completions/scoop/scoop-completions.nu

@@ -92,13 +92,29 @@ def scoopShimBuilds [] {
 }
 
 def scoopCommands [] {
-  ^powershell -nop -nol -c "(scoop help | ConvertTo-Json -Compress)"
-  | decode
-  | lines
-  | last
-  | to text
-  | from json
-  | rename value description
+  let libexecDir = if ('SCOOP' in $env) {
+    [ $env.SCOOP, 'apps', 'scoop', 'current', 'libexec' ] | path join
+  } else {
+    [ $env.USERPROFILE, 'scoop', 'apps', 'scoop', 'current', 'libexec' ] | path join
+  }
+
+  let commands = (
+   ls $libexecDir
+   | each {|command|
+       [
+         [value, description];
+         [
+           # eg. scoop-help.ps1 -> help
+           ($command.name | path basename | str substring 6..-4),
+           # second line is starts with '# Summary: '
+           # eg. '# Summary: Install apps' -> 'Install apps'
+           (open $command.name | lines | skip 1 | first | str substring 11..)
+         ]
+       ]
+     }
+   | flatten
+  )
+  $commands
 }
 
 def scoopAliases [] {