http: optimize HTTP request thread we don't need a mutex at all, in fact all we need is an atomic boolean to signify whether the thread is cancelled. curl options are now for the most part handled by a separate function to keep them in sync between non-threaded and threaded implementations

#include <fmt/compile.h>

__attribute__((visibility("default"))) std::string foo() {
  return fmt::format(FMT_COMPILE("foo bar {}"), 4242);
}