Support nested partitions and partitions directly targeting services (#122)

* Do the nested partition thing

* Tidy up touched code

* Add nested partition test project, not fully functional

* Clean up variable names, move path_metadata mutation strictly into snapshot_reconciler

* Remove path_metadata, snapshotting is now pure

* Factor out snapshot metadata storage to fix a missing case

* Pull instance_name out of per_path_metadata, closer to what we need

* Refactor to make metadata make more sense, part one

* All appears to be well

* Cull 'metadata_per_path' in favor of 'instances_per_path'

* Remove SnapshotContext

* InstanceMetadata -> PublicInstanceMetadata in web module

* Build in snapshot testing system for testing... snapshots?

* Remove pretty_assertions to see if it fixes a snapshot comparison bug

* Reintroduce pretty assertions, it's not the cause of inequality

* Fix snapshot tests with custom relative path serializer

server/src/visualize.rs

@@ -11,7 +11,7 @@ use rbx_tree::RbxId;
 use crate::{
     imfs::{Imfs, ImfsItem},
     rbx_session::RbxSession,
-    web::InstanceMetadata,
+    web::PublicInstanceMetadata,
 };
 
 static GRAPHVIZ_HEADER: &str = r#"
@@ -74,7 +74,7 @@ fn visualize_rbx_node(session: &RbxSession, id: RbxId, output: &mut fmt::Formatt
     let mut node_label = format!("{}|{}|{}", node.name, node.class_name, id);
 
     if let Some(session_metadata) = session.get_instance_metadata(id) {
-        let metadata = InstanceMetadata::from_session_metadata(session_metadata);
+        let metadata = PublicInstanceMetadata::from_session_metadata(session_metadata);
         node_label.push('|');
         node_label.push_str(&serde_json::to_string(&metadata).unwrap());
     }