fix: handle invalid duration humanize

[DeoJin]

Summary

Return \invalid duration\ from \duration.humanize()\ when the duration value is not finite, instead of letting relative-time formatting turn \NaN\ into an incorrect humanized string.

Changes

• guard \Duration#humanize\ against non-finite millisecond values
• add regression coverage for \dayjs.duration(NaN).humanize()\ with and without suffixes

Testing

• 
  px jest test/plugin/duration.test.js --runInBand\

Fixes #3006