binary:encode_unsigned/1 BIF

[KronicDeth]

binary:encode_unsigned/1 BIF is needed by lib/ssh/src/ssh_bits.erl

cargo test --package liblumen_otp lumen::otp::lib::ssh::ssh_bits

[mlwilkerson]

@KronicDeth whoops, just realized you'd self-assigned this as I submitted a draft PR for it. I'll back away if you prefer. I just picked this one to work on cause it was the first one I noticed that looked doable.