allow into duration to take an integer amount of ns (#10286)

related to
-
https://discord.com/channels/601130461678272522/615329862395101194/1149717458786197524

# Description
because `1_234 | into datetime` takes an integer number of `ns` and
`1_234 | into filesize` takes an integer amount of bytes, i think `1_234
| into duration` should also be valid and see `1_234` as an integer
amount of `ns` 😋

# User-Facing Changes
## before
either
```nushell
1234 | into string | $in ++ "ns" | into duration
```
```nushell
1234 | $"($in)ns" | into duration
```
or
```nushell
1234 * 1ns
```
and
```nushell
> 1_234 | into duration
Error: nu::parser::input_type_mismatch

  × Command does not support int input.
   ╭─[entry #2:1:1]
 1 │ 1_234 | into duration
   ·         ──────┬──────
   ·               ╰── command doesn't support int input
   ╰────
```

## after
```nushell
> 1_234 | into duration
1µs 234ns
```

# Tests + Formatting
new example test
```rust
Example {
    description: "Convert a number of ns to duration",
    example: "1_234_567 | into duration",
    result: Some(Value::duration(1_234_567, span)),
}
```

# After Submitting

crates/nu-command/src/conversions/into/duration.rs

@@ -19,6 +19,7 @@ impl Command for SubCommand {
     fn signature(&self) -> Signature {
         Signature::build("into duration")
             .input_output_types(vec![
+                (Type::Int, Type::Duration),
                 (Type::String, Type::Duration),
                 (Type::Duration, Type::Duration),
                 (Type::Table(vec![]), Type::Table(vec![])),
@@ -26,6 +27,12 @@ impl Command for SubCommand {
                 //(Type::Record(vec![]), Type::Record(vec![])),
             ])
             //.allow_variants_without_examples(true)
+            .named(
+                "unit",
+                SyntaxShape::String,
+                "Unit to convert number into (will have an effect only with integer input)",
+                Some('u'),
+            )
             .rest(
                 "rest",
                 SyntaxShape::CellPath,
@@ -107,6 +114,16 @@ impl Command for SubCommand {
                 example: "420sec | into duration",
                 result: Some(Value::duration(7 * 60 * NS_PER_SEC, span)),
             },
+            Example {
+                description: "Convert a number of ns to duration",
+                example: "1_234_567 | into duration",
+                result: Some(Value::duration(1_234_567, span)),
+            },
+            Example {
+                description: "Convert a number of an arbitraty unit to duration",
+                example: "1_234 | into duration --unit ms",
+                result: Some(Value::duration(1_234 * 1_000_000, span)),
+            },
         ]
     }
 }
@@ -123,15 +140,39 @@ fn into_duration(
     };
     let column_paths: Vec<CellPath> = call.rest(engine_state, stack, 0)?;
 
+    let unit = match call.get_flag::<String>(engine_state, stack, "unit")? {
+        Some(sep) => {
+            if ["ns", "us", "µs", "ms", "sec", "min", "hr", "day", "wk"]
+                .iter()
+                .any(|d| d == &sep)
+            {
+                sep
+            } else {
+                return Err(ShellError::CantConvertToDuration {
+                    details: sep,
+                    dst_span: span,
+                    src_span: span,
+                    help: Some(
+                        "supported units are ns, us/µs, ms, sec, min, hr, day, and wk".to_string(),
+                    ),
+                });
+            }
+        }
+        None => "ns".to_string(),
+    };
+
     input.map(
         move |v| {
             if column_paths.is_empty() {
-                action(&v, span)
+                action(&v, &unit.clone(), span)
             } else {
+                let unitclone = &unit.clone();
                 let mut ret = v;
                 for path in &column_paths {
-                    let r =
-                        ret.update_cell_path(&path.members, Box::new(move |old| action(old, span)));
+                    let r = ret.update_cell_path(
+                        &path.members,
+                        Box::new(move |old| action(old, unitclone, span)),
+                    );
                     if let Err(error) = r {
                         return Value::error(error, span);
                     }
@@ -202,7 +243,7 @@ fn string_to_duration(s: &str, span: Span) -> Result<i64, ShellError> {
     })
 }
 
-fn action(input: &Value, span: Span) -> Value {
+fn action(input: &Value, unit: &str, span: Span) -> Value {
     let value_span = input.span();
     match input {
         Value::Duration { .. } => input.clone(),
@@ -210,6 +251,20 @@ fn action(input: &Value, span: Span) -> Value {
             Ok(val) => Value::duration(val, span),
             Err(error) => Value::error(error, span),
         },
+        Value::Int { val, .. } => {
+            let ns = match unit {
+                "ns" => 1,
+                "us" | "µs" => 1_000,
+                "ms" => 1_000_000,
+                "sec" => NS_PER_SEC,
+                "min" => NS_PER_SEC * 60,
+                "hr" => NS_PER_SEC * 60 * 60,
+                "day" => NS_PER_SEC * 60 * 60 * 24,
+                "wk" => NS_PER_SEC * 60 * 60 * 24 * 7,
+                _ => 0,
+            };
+            Value::duration(*val * ns, span)
+        }
         // Propagate errors by explicitly matching them before the final case.
         Value::Error { .. } => input.clone(),
         other => Value::error(
@@ -253,7 +308,11 @@ mod test {
     #[case("14ns 3hr 17sec", 14 + 3 * 3600 * NS_PER_SEC + 17 * NS_PER_SEC)] // compound string with units in random order
 
     fn turns_string_to_duration(#[case] phrase: &str, #[case] expected_duration_val: i64) {
-        let actual = action(&Value::test_string(phrase), Span::new(0, phrase.len()));
+        let actual = action(
+            &Value::test_string(phrase),
+            "ns",
+            Span::new(0, phrase.len()),
+        );
         match actual {
             Value::Duration {
                 val: observed_val, ..