fix(date): zero-pad milliseconds when formatting %N fractional seconds (#929)

%N renders the fractional part of the second. The milliseconds returned by
getMilliseconds() are the three most significant digits of that fraction and
must be zero-padded to three digits before use, otherwise sub-100ms values
lose their leading zeros:

  50ms => strftime("%N")  returned "500000000", expected "050000000"
   5ms => strftime("%3N") returned "500",       expected "005"

Pad the milliseconds to three digits before slicing to the requested width.

src/util/strftime.ts

@@ -98,7 +98,7 @@ const formatCodes: Record<string, FormatCodeHandler> = {
   M: (d: LiquidDate) => d.getMinutes(),
   N: (d: LiquidDate, opts: FormatOptions) => {
     const width = Number(opts.width) || 9
-    const str = String(d.getMilliseconds()).slice(0, width)
+    const str = padStart(String(d.getMilliseconds()), 3, '0').slice(0, width)
     opts.memoryLimit?.use(width - str.length)
     return padEnd(str, width, '0')
   },