Keep track of State at event for state resolution

feat: first steps towards joining rooms over federation
Add state-res as a dependency of conduit
Add reverse_topological_power_sort before append_pdu
Implement statehashstatid_pduid tree for keeping track of state
Clean up implementation of state_hash as key for tracking state

src/utils.rs

@@ -1,3 +1,4 @@
+use crate::Error;
 use argon2::{Config, Variant};
 use cmp::Ordering;
 use rand::prelude::*;
@@ -90,3 +91,8 @@ pub fn common_elements(
             .all(|b| b)
     }))
 }
+
+pub fn deserialize<'de, T: serde::Deserialize<'de>>(val: &'de sled::IVec) -> Result<T, Error> {
+    serde_json::from_slice::<T>(val.as_ref())
+        .map_err(|_| Error::bad_database("PDU in db is invalid."))
+}