Stylua formatting (#785)

Uses Stylua to format all existing Lua files, and adds a CI check in
`lint` to pin this improvement. Excludes formatting dependencies, of
course.

.github/workflows/ci.yml

@@ -42,7 +42,7 @@ jobs:
       run: cargo test --locked --verbose
 
   lint:
-    name: Rustfmt and Clippy
+    name: Rustfmt, Clippy, & Stylua
     runs-on: ubuntu-latest
 
     steps:
@@ -62,6 +62,9 @@ jobs:
       with:
         version: 'v0.2.7'
 
+    - name: Stylua
+      run: stylua --check plugin/src
+
     - name: Rustfmt
       run: cargo fmt -- --check