message: Add `std` config for `SchemaGenerator` for `ProtocolVersion`.
diff: @@ -2,6 +2,7 @@ use alloc::vec::Vec;
  use core::fmt;
  use datasize::DataSize;
  +#[cfg(feature = "std")]
  use schemars::{gen::SchemaGenerator, schema::Schema, JsonSchema};
  use serde::{Deserialize, Serialize};
  @@ -162,6 +163,7 @@ impl fmt::Display for ProtocolVersion {
  }
  }
  +#[cfg(feature = "std")]
  impl JsonSchema for ProtocolVersion {
  fn schema_name() -> String {
  String::from("ProtocolVersion")
  