small, backwards compatible enhancements to std (#14763)

# Description
Small, backwards compatible enhancements to the standard library.

# User-Facing Changes

- changed `iter find`, `iter find-index`: Only consume the input stream
up to the first match.
- added `log set-level`: a small convenience command for setting the log
level
- added `$null_device`: `null-device` as a const variable, would allow
conditional sourcing if #13872 is fixed

# Tests + Formatting

- 🟢 toolkit fmt
- 🟢 toolkit clippy
- 🟢 toolkit test
- 🟢 toolkit test stdlib

# After Submitting
N/A

crates/nu-std/std/bench/mod.nu

@@ -41,21 +41,21 @@ export def main [
     --verbose (-v) # be more verbose (namely prints the progress)
     --pretty # shows the results in human-readable format: "<mean> +/- <stddev>"
 ] {
-    let times = (
+    let times: list<duration> = (
         seq 1 $rounds | each {|i|
             if $verbose { print -n $"($i) / ($rounds)\r" }
-            timeit { do $code } | into int | into float
+            timeit { do $code }
         }
     )
 
     if $verbose { print $"($rounds) / ($rounds)" }
 
     let report = {
-        mean: ($times | math avg | from ns)
-        min: ($times | math min | from ns)
-        max: ($times | math max | from ns)
-        std: ($times | math stddev | from ns)
-        times: ($times | each { from ns })
+        mean: ($times | math avg)
+        min: ($times | math min)
+        max: ($times | math max)
+        std: ($times | into int | math stddev | into int | into duration)
+        times: ($times)
     }
 
     if $pretty {
@@ -64,8 +64,3 @@ export def main [
         $report
     }
 }
-
-# convert an integer amount of nanoseconds to a real duration
-def "from ns" [] {
-    [$in "ns"] | str join | into duration
-}