Use B-tree collections instead of Fx hash ones

This removes a dependency. Since the collections in question should
usually be pretty small, it might also reduce memory overhead at little
cost in speed. Here are some relevant performance discussions:

  https://users.rust-lang.org/t/hashmap-vs-btreemap/13804
  https://www.reddit.com/r/rust/comments/7rgowj/hashmap_vs_btreemap/

app-proto/Cargo.lock

@@ -89,7 +89,6 @@ dependencies = [
  "lazy_static",
  "nalgebra",
  "readonly",
- "rustc-hash",
  "sycamore",
  "wasm-bindgen-test",
  "web-sys",
@@ -364,12 +363,6 @@ dependencies = [
  "syn",
 ]
 
-[[package]]
-name = "rustc-hash"
-version = "2.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "583034fd73374156e66797ed8e5b0d5690409c9226b22d87cb7f19821c05d152"
-
 [[package]]
 name = "safe_arch"
 version = "0.7.2"