Add Filesize type (#14369)

# Description
Adds a new `Filesize` type so that `FromValue` can be used to convert a
`Value::Filesize` to a `Filesize`. Currently, to extract a filesize from
a `Value` using `FromValue`, you have to extract an `i64` which coerces
`Value::Int`, `Value::Duration`, and `Value::Filesize` to an `i64`.

Having a separate type also allows us to enforce checked math to catch
overflows. Similarly, it allows us to specify other trait
implementations like `Display` in a common place.

# User-Facing Changes
Multiplication with filesizes now error on overflow. Should not be a
breaking change for plugins (i.e., serialization) since `Filesize` is
marked with `serde(transparent)`.

# Tests + Formatting
Updated some tests.

crates/nu-command/tests/format_conversions/nuon.rs

@@ -5,9 +5,9 @@ fn to_nuon_correct_compaction() {
     let actual = nu!(
         cwd: "tests/fixtures/formats", pipeline(
         r#"
-            open appveyor.yml 
-            | to nuon 
-            | str length 
+            open appveyor.yml
+            | to nuon
+            | str length
             | $in > 500
         "#
     ));