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-cmd-extra/src/extra/bits/into.rs

@@ -203,7 +203,7 @@ pub fn action(input: &Value, _args: &Arguments, span: Span) -> Value {
             Value::string(raw_string.trim(), span)
         }
         Value::Int { val, .. } => convert_to_smallest_number_type(*val, span),
-        Value::Filesize { val, .. } => convert_to_smallest_number_type(*val, span),
+        Value::Filesize { val, .. } => convert_to_smallest_number_type(val.get(), span),
         Value::Duration { val, .. } => convert_to_smallest_number_type(*val, span),
         Value::String { val, .. } => {
             let raw_bytes = val.as_bytes();

crates/nu-cmd-extra/src/extra/conversions/fmt.rs

@@ -66,7 +66,7 @@ fn action(input: &Value, _args: &CellPathOnlyArgs, span: Span) -> Value {
     match input {
         Value::Float { val, .. } => fmt_it_64(*val, span),
         Value::Int { val, .. } => fmt_it(*val, span),
-        Value::Filesize { val, .. } => fmt_it(*val, span),
+        Value::Filesize { val, .. } => fmt_it(val.get(), span),
         // Propagate errors by explicitly matching them before the final case.
         Value::Error { .. } => input.clone(),
         other => Value::error(