chore: specify more paths in .prettierignore (#10933)

Prettier is a tool with questionable defaults and performance. Not only
is it slow to format files, but it also doesn't respect nested
`.gitignore` or `.prettierignore` files. This means we need to specify
all paths that it should not touch in the top-level .`prettierignore` to
get even close to acceptable performance. Even with these optimisations,
it still takes around 8 seconds to format our workspace.

.prettierignore

@@ -1,17 +1,23 @@
 elixir/_build
 elixir/deps
 elixir/apps/web/assets
+elixir/.elixir_ls
 rust/target
 kotlin/android/app/build
+kotlin/android/.gradle
+kotlin/android/.kotlin
+kotlin/android/build
 website/node_modules
 website/.next
+website/timestamps.json
 **/*.sh
 **/*.ex
 **/*.rs
 **/*.wxs
 **/pnpm-lock.yaml
-.github/pnpm-lock.yaml
 swift/apple/**/Contents.json
 rust/gui-client/src-frontend/generated
 rust/gui-client/dist
 rust/gui-client/node_modules
+rust/gui-client/src-tauri/gen
+rust/gui-client/.flowbite-react/class-list.json