[Fuzzing X64] [Copilot] Add Base64 parity APIs with Base64Url

For all the logs, see https://mihubot.xyz/api/RuntimeUtils/Jobs/Progress?jobId=FEaae6I

Tracking issue: https://github.com/MihuBot/runtime-utils/issues/1712

Started at 2026-01-14 15-51-40 UTC, ran for 36 minutes 8 seconds.