message: [pdsl_core] Add no_std boilerplate to enzyme
  Also replace std::sync::Mutex with spin::Mutex from crates.io for no_std compatibility.
  We still should search for a better alternative.
diff: +#![feature(alloc_error_handler)]
  +#![feature(core_intrinsics)]
  #![feature(alloc)]
  +#![no_std]
  +
  #[cfg(all(test, feature = "test-env"))]
  mod tests;
  +#[cfg_attr(test, macro_use)]
  +extern crate alloc;
  +
  +use alloc::string::String;
  +use alloc::vec::Vec;
  +
  pub mod utils;
  use pdsl_core::storage;
  use parity_codec_derive::{Encode, Decode};
  +// Use `wee_alloc` as the global allocator.
  +#[global_allocator]
  +static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;
  +
  /// A tweet done by a registered user.
  #[derive(Debug, Clone, PartialEq, Eq)]
  #[derive(Encode, Decode)]
  