FEATURE: add the bench command to the standard library (#8969)

Should address the first point of
- https://github.com/nushell/nushell/issues/8696.

# Description
i've seen a few appearances of this `benchmark` idea in recent works on
`nu-std`, so i thought it would be great to add it finally.

# User-Facing Changes
a new `std bench` command to measure the performance of `nushell`
closures and code blocks.

# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- ⚫ `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting
```
$nothing
```

crates/nu-std/lib/mod.nu

@@ -148,3 +148,73 @@ export def clip [
         notify-send "std clip" "saved to clipboard"
     }
 }
+
+# convert an integer amount of nanoseconds to a real duration
+def "from ns" [] {
+    [$in "ns"] | str join | into duration
+}
+
+# run a piece of `nushell` code multiple times and measure the time of execution.
+#
+# this command returns a benchmark report of the following form:
+# ```
+# record<
+#   mean: duration
+#   std: duration
+#   times: list<duration>
+# >
+# ```
+#
+# > **Note**  
+# > `std bench --pretty` will return a `string`.
+#
+# # Examples
+#     measure the performance of simple addition
+#     > std bench { 1 + 2 } -n 10
+#     ╭───────┬────────────────────╮
+#     │ mean  │ 4µs 956ns          │
+#     │ std   │ 4µs 831ns          │
+#     │       │ ╭───┬────────────╮ │
+#     │ times │ │ 0 │ 19µs 402ns │ │
+#     │       │ │ 1 │  4µs 322ns │ │
+#     │       │ │ 2 │  3µs 352ns │ │
+#     │       │ │ 3 │  2µs 966ns │ │
+#     │       │ │ 4 │        3µs │ │
+#     │       │ │ 5 │   3µs 86ns │ │
+#     │       │ │ 6 │   3µs 84ns │ │
+#     │       │ │ 7 │  3µs 604ns │ │
+#     │       │ │ 8 │   3µs 98ns │ │
+#     │       │ │ 9 │  3µs 653ns │ │
+#     │       │ ╰───┴────────────╯ │
+#     ╰───────┴────────────────────╯
+#
+#     get a pretty benchmark report
+#     > std bench { 1 + 2 } --pretty
+#     3µs 125ns +/- 2µs 408ns
+export def bench [
+    code: closure  # the piece of `nushell` code to measure the performance of
+    --rounds (-n): int = 50  # the number of benchmark rounds (hopefully the more rounds the less variance)
+    --verbose (-v): bool  # be more verbose (namely prints the progress)
+    --pretty: bool  # shows the results in human-readable format: "<mean> +/- <stddev>"
+] {
+    let times = (
+        seq 1 $rounds | each {|i|
+            if $verbose { print -n $"($i) / ($rounds)\r" }
+            timeit { do $code } | into int | into decimal
+        }
+    )
+
+    if $verbose { print $"($rounds) / ($rounds)" }
+
+    let report = {
+        mean: ($times | math avg | from ns)
+        std: ($times | math stddev | from ns)
+        times: ($times | each { from ns })
+    }
+
+    if $pretty {
+        $"($report.mean) +/- ($report.std)"
+    } else {
+        $report
+    }
+}