Remove runtime dependency on base64

[Earlopain]

Ruby 3.3 prints a warning if base64 is used without specifying it in the gemfile. Ruby 3.4 will error.
Since it's just a wrapper around the pack/unpack methods it's trivial to replace.

You don't see this in CI since the Gemfile contains dependencies that in turn already depend on base64, like activesupport.

Here is some similar work:

• Remove base64 dependency rack/rack#2110
• [Fix #12310] Drop base64 gem from runtime dependency rubocop/rubocop#12313
• Remove dependency on base64 gem sidekiq/sidekiq#6151
• Remove dependency on the base64 gem opensearch-project/opensearch-ruby#221
• Remove runtime dependency on base64 lostisland/faraday#1541
• Remove runtime dependency on base64 newrelic/newrelic-ruby-agent#2378

[ddnexus]

Thank you!

[Earlopain]

New release already, very cool!