Add `simdjson_free_memory(): int`

[TysonAndre]

This may be useful if applications parse megabytes of json on startup, but don't use simdjson for large requests later on.

This would free the buffers used by the underlying C simdjson library

[TysonAndre]

simdjson_warn_unused
inline error_code dom_parser_implementation::allocate(size_t capacity, size_t max_depth) noexcept {
  if (this->max_depth() != max_depth) {
    error_code err = set_max_depth(max_depth);
    if (err) { return err; }
  }
  if (_capacity != capacity) {
    error_code err = set_capacity(capacity);
    if (err) { return err; }
  }
  return SUCCESS;
}

Most of the memory can be freed without this as a workaround by calling simdjson_decode('""') as a side effect of how the C library is implemented - it will always change the depth/capacity