Change distance evaluation period from Sessions to Blocks

Closes #202 (closed) Closes #207 (closed)

• Create evaluation period in block.
• Update tests.
• Weight accounting
• Upgrade the distance oracle.
• Fix #207 (closed).
• Closes #174 (closed): the worst and simplest estimation equates to one evaluation being 0.0037% of a block's weight, based on the current reference machine. To maintain a reasonable load on the system, it's advisable that the cumulative weight of all evaluations does not surpass 5-10% of a block's capacity. Consequently, setting MAX_EVALUATIONS_PER_SESSION between 1 300 and 2 600 would ensure safe operation.

distance-oracle/src/api.rs

@@ -40,35 +40,35 @@ pub async fn parent_hash(client: &Client) -> H256 {
         .hash()
 }
 
-pub async fn current_session(client: &Client, parent_hash: H256) -> u32 {
+pub async fn current_pool_index(client: &Client, parent_hash: H256) -> u32 {
     client
         .storage()
         .at(parent_hash)
-        .fetch(&runtime::storage().session().current_index())
+        .fetch(&runtime::storage().distance().current_pool_index())
         .await
-        .expect("Cannot fetch current session")
+        .expect("Cannot fetch current pool index")
         .unwrap_or_default()
 }
 
 pub async fn current_pool(
     client: &Client,
     parent_hash: H256,
-    current_session: u32,
+    current_pool_index: u32,
 ) -> Option<runtime::runtime_types::pallet_distance::types::EvaluationPool<AccountId, IdtyIndex>> {
     client
         .storage()
         .at(parent_hash)
-        .fetch(&match current_session % 3 {
+        .fetch(&match current_pool_index {
             0 => {
-                debug!("Looking at Pool1 for session {}", current_session);
+                debug!("Looking at Pool1 for pool index {}", current_pool_index);
                 runtime::storage().distance().evaluation_pool1()
             }
             1 => {
-                debug!("Looking at Pool2 for session {}", current_session);
+                debug!("Looking at Pool2 for pool index {}", current_pool_index);
                 runtime::storage().distance().evaluation_pool2()
             }
             2 => {
-                debug!("Looking at Pool0 for session {}", current_session);
+                debug!("Looking at Pool0 for pool index {}", current_pool_index);
                 runtime::storage().distance().evaluation_pool0()
             }
             _ => unreachable!("n%3<3"),