try to fix datetime-diff for ms, us, ns (#15537)

# Description

This PR tries to fix the datetime-diff custom command so that it
includes ms, us, ns.

Difference in the banner in 2 separate starts.

### Old
```nushell
It's been this long since Nushell's first commit:
5yrs 10months 29days 9hrs 1min 47secs
```

### New
```nushell
It's been this long since Nushell's first commit:
5yrs 10months 29days 9hrs 1min 22secs 49ms 885µs
```

There should be ns above on the new one, not sure why there isn't. It
could have something to do with how the banner works but i'll save that
for another PR.

🤔 It could be because there are no fractional seconds in the math?
`datetime-diff (date now) 2019-05-10T09:59:12-07:00`. However, I'm not
sure why `date now` has no nanoseconds. Oh, wait. I think that's because
MacOS doesn't have nanosecond precision?
```
❯ ^date +%s.%N
1744251636.365003000
```

Closes https://github.com/nushell/nushell/issues/15524

/cc @NotTheDr01ds 

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crates/nu-std/std/dt/mod.nu

@@ -79,7 +79,7 @@ def borrow-minute [from: record, current: record] {
 
 def borrow-second [from: record, current: record] {
     mut current = $current
-    $current.nanosecond = $current.nanosecond + 1_000_000_000
+    $current.millisecond = $current.millisecond + 1_000
     $current.second = $current.second - 1
     if $current.second < 0 {
         $current = (borrow-minute $from $current)
@@ -88,19 +88,41 @@ def borrow-second [from: record, current: record] {
     $current
 }
 
+def borrow-millisecond [from: record, current: record] {
+    mut current = $current
+    $current.microsecond = $current.microsecond + 1_000
+    $current.millisecond = $current.millisecond - 1
+    if $current.millisecond < 0 {
+        $current = (borrow-second $from $current)
+    }
+
+    $current
+}
+
+def borrow-microsecond [from: record, current: record] {
+    mut current = $current
+    $current.nanosecond = $current.nanosecond + 1_000
+    $current.microsecond = $current.microsecond - 1
+    if $current.microsecond < 0 {
+        $current = (borrow-millisecond $from $current)
+    }
+
+    $current
+}
+
 # Subtract later from earlier datetime and return the unit differences as a record
 @example "Get the difference between two dates" {
-    dt datetime-diff 2023-05-07T04:08:45+12:00 2019-05-10T09:59:12-07:00
+    dt datetime-diff 2023-05-07T04:08:45.582926123+12:00 2019-05-10T09:59:12.967486456-07:00
 } --result {
     year: 3,
     month: 11,
     day: 26,
     hour: 23,
     minute: 9,
-    second: 33,
-    millisecond: 0,
-    microsecond: 0,
-    nanosecond: 0,
+    second: 32,
+    millisecond: 615,
+    microsecond: 439,
+    nanosecond: 667,
 }
 export def datetime-diff [
     later: datetime, # a later datetime
@@ -149,14 +171,20 @@ export def datetime-diff [
         $result = (borrow-minute $from_expanded $result)
     }
 
-    $result.nanosecond = $from_expanded.nanosecond - $to_expanded.nanosecond
-    if $result.nanosecond < 0 {
+    $result.millisecond = $from_expanded.millisecond - $to_expanded.millisecond
+    if $result.millisecond < 0 {
         $result = (borrow-second $from_expanded $result)
     }
 
-    $result.millisecond = ($result.nanosecond / 1_000_000 | into int) # don't want a float
-    $result.microsecond = (($result.nanosecond mod 1_000_000) / 1_000 | into int)
-    $result.nanosecond = ($result.nanosecond mod 1_000 | into int)
+    $result.microsecond = $from_expanded.microsecond - $to_expanded.microsecond
+    if $result.microsecond < 0 {
+        $result = (borrow-millisecond $from_expanded $result)
+    }
+
+    $result.nanosecond = $from_expanded.nanosecond - $to_expanded.nanosecond
+    if $result.nanosecond < 0 {
+        $result = (borrow-microsecond $from_expanded $result)
+    }
 
     $result
 }

crates/nu-std/tests/test_dt.nu

@@ -34,6 +34,13 @@ def earlier_arg_must_be_less_or_equal_later [] {
     assert error {|| (datetime-diff $t1 $t2)} 
 }
 
+@test
+def banner_math_with_ms_us_ns [] {
+    let t1 = 2023-05-07T04:08:45.582926123+12:00
+    let t2 = 2019-05-10T09:59:12.967486456-07:00
+    assert equal (datetime-diff $t1 $t2) ({year:3, month:11, day:26, hour:23, minute:9, second:32, millisecond:615, microsecond:439 nanosecond:667})
+}
+
 @test
 def pp_skips_zeros [] {
     assert equal (pretty-print-duration {year:1, month:0, day:0, hour:0, minute:0, second:0, millisecond:0, microsecond:0 nanosecond:0}) "1yr "