Implement Readable/Writeable for RwLock wrappers

We now support separate R/W locks in `LockableScore`, which allow
us to do routefinding in parallel, however in order to support
`WriteableScore` for such users we need to implement `Writeable`
for `RwLock` wrappers around `Writeable` types, which we do here.

Author: TheBlueMatt

lightning/src/util/ser.rs

@@ -17,7 +17,7 @@ use crate::prelude::*;
 use crate::io::{self, Read, Seek, Write};
 use crate::io_extras::{copy, sink};
 use core::hash::Hash;
-use crate::sync::Mutex;
+use crate::sync::{Mutex, RwLock};
 use core::cmp;
 use core::convert::TryFrom;
 use core::ops::Deref;
@@ -1195,6 +1195,18 @@ impl<T: Writeable> Writeable for Mutex<T> {
 	}
 }
 
+impl<T: Readable> Readable for RwLock<T> {
+	fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
+		let t: T = Readable::read(r)?;
+		Ok(RwLock::new(t))
+	}
+}
+impl<T: Writeable> Writeable for RwLock<T> {
+	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+		self.read().unwrap().write(w)
+	}
+}
+
 impl<A: Readable, B: Readable> Readable for (A, B) {
 	fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
 		let a: A = Readable::read(r)?;