refactor(backend): uses new streamlined latency.Matrix to add delay

This replaces the old multi-map-based location and latencies lookups
that were a bit awkward to work with.

This removes the existing map[string]map[string]time.Duration{}
latencies using the data in the internal/latency package.

The new latency package provides the lm.Latency(a, b) to get the
latency between two hotstuff.IDs.

We now only need to fill the Locations []string in the ReplicaOpts
to pass the set of locations around.

.vscode/settings.json

@@ -1,5 +1,5 @@
 {
-	"clang-format.style": "{ IndentWidth: 4, BasedOnStyle: google, AlignConsecutiveAssignments: true, ColumnLimit: 120 }",
+	"clang-format.style": "{ IndentWidth: 2, BasedOnStyle: google, AlignConsecutiveAssignments: true, ColumnLimit: 120 }",
 	"editor.formatOnSave": true,
 	"files.insertFinalNewline": true,
 	"protoc": {