Bump llhttp-ffi (0.5.0)

[bryanp]

Updates the llhttp-ffi dependency to v0.5.0. The only difference is that it now uses lhttp v8.1.0, the latest release.

[bryanp]

Note I am seeing one test failure on this branch but also see it in main:

1) HTTP::Options headers accepts any object that respond to :to_hash
     Failure/Error: x = Struct.new(:to_hash).new("accept" => "json")

     ArgumentError:
       unknown keywords: accept
     # ./spec/lib/http/options/headers_spec.rb:17:in `initialize'
     # ./spec/lib/http/options/headers_spec.rb:17:in `new'
     # ./spec/lib/http/options/headers_spec.rb:17:in `block (2 levels) in <top (required)>'