fix: use custom base64 decoder to workaround deno bug

[markwylde]

This PR works around issue https://github.com/denodrivers/mongo/issues/381, a bug that appears to be in Deno: https://github.com/denoland/deno/issues/19546

It uses a custom base64 function, but maybe we could find another library out there that doesn't use the built in atob.

[lucsoft]

Wait does the std base64 encoder also has this issue or just atob?

[markwylde]

Yeah the std base64 encoder uses atob [1], which it looks like is broken unless I've misunderstood.

1. https://github.com/denoland/deno_std/blob/main/encoding/base64.ts#L151

[markwylde]

this is not a fix this is a feature request. is this per spec? 😄 Hope we can resolve this together :)

if you have any questions feel free to ask

Sorry, I'm happy to rebase to any commit message appropriate for this.

[opimand]

Some fix? Can't use Mongo with Deno by default