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

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

Tracking issue: https://github.com/MihuBot/runtime-utils/issues/1713

Started at 2026-01-14 16-48-54 UTC, ran for 35 minutes 26 seconds.