Support jruby

[mensfeld]

I run tests on most recent jruby stable and FFI aside from one case (fixable) works ok. We could rollout the jruby support easily.

[headius]

I look forward to playing with benchmarks and seeing how we can make the JRuby support superfast!

[mensfeld]

Things we need to do to make this happen:

• Fix segfaults related to oauth bearear callback assignments
• Ignore fork specs for jruby
• Benchmark performance and check if it makes sense (at least 50k msg/s passthrough, ideally more than 100k)

[headius]

oauth bearear callback assignments

FFI? There's at least one known JRuby issue with FFI callbacks on Apple Silicon that requires some low-level C work (probably by me 😭).

[mensfeld]

@headius, the thing is, other callbacks work as expected, so I think it's rather a misuse/misconfiguration. I'll get back to you next week when I look into this with more info.