fix: enable serde alloc feature for no_std builds

#[serde(flatten)] on CommonFields requires serde's alloc feature,
which was never activated for the no_std (embassy-rt) build path.
The std feature enables serde/std (which implies alloc), masking
the issue for default builds. Also add Box imports needed for the
boxed error variants in no_std context.

Author: e-desouza

Cargo.toml

@@ -56,7 +56,7 @@ chrono = { version = "0.4.19", default-features = false, features = [
 ] }
 hex = { version = "0.4.3", default-features = false, features = ["alloc"] }
 rand = { version = "0.8.5", default-features = false, features = ["getrandom"] }
-serde = { version = "1.0.130", default-features = false, features = ["derive"] }
+serde = { version = "1.0.130", default-features = false, features = ["derive", "alloc"] }
 serde_json = { version = "1.0.68", default-features = false, features = [
     "alloc",
 ] }

src/asynch/clients/exceptions.rs

@@ -1,3 +1,4 @@
+use alloc::boxed::Box;
 use thiserror_no_std::Error;
 
 #[cfg(feature = "helpers")]

src/models/results/mod.rs

@@ -43,6 +43,7 @@ pub mod unsubscribe;
 use super::{requests::XRPLRequest, Amount, XRPLModelException, XRPLModelResult};
 use alloc::{
     borrow::Cow,
+    boxed::Box,
     string::{String, ToString},
 };
 use core::convert::{TryFrom, TryInto};