burrego: implement missing Token Verification builtins

[flavio]

Epic: #56

These are the builtins that burrego has to provide that belong to the Token Verification area:

• io.jwt.verify_rs256
• io.jwt.verify_rs384
• io.jwt.verify_rs512
• io.jwt.verify_ps256
• io.jwt.verify_ps256
• io.jwt.verify_ps384
• io.jwt.verify_ps512
• io.jwt.verify_es256
• io.jwt.verify_es384
• io.jwt.verify_es512
• io.jwt.verify_hs384
• io.jwt.verify_hs512
• io.jwt.decode
• io.jwt.decode_verify