Update TypeScript to 5.9.3 and fix type errors

Co-authored-by: kentcdodds <[email protected]>

Author: Copilot

.github/workflows/validate.yml

@@ -16,7 +16,7 @@ jobs:
     if: ${{ !contains(github.head_ref, 'all-contributors') }}
     strategy:
       matrix:
-        node: [16, 18]
+        node: [lts/-1, lts/*]
     runs-on: ubuntu-latest
     steps:
       - name: 🛑 Cancel Previous Runs
@@ -63,7 +63,7 @@ jobs:
       - name: ⎔ Setup node
         uses: actions/setup-node@v6
         with:
-          node-version: 18
+          node-version: lts/*
 
       - name: 📥 Download deps
         uses: bahmutov/npm-install@v1

package.json

@@ -48,7 +48,7 @@
     "kcd-scripts": "^12.2.0",
     "remark": "^14.0.2",
     "remark-html": "^15.0.1",
-    "typescript": "^4.7.4"
+    "typescript": "^5.9.3"
   },
   "peerDependencies": {
     "@remark-embedder/core": "^3.0.0"

src/__tests__/index.ts

@@ -12,12 +12,14 @@ const unquoteSerializer = {
 expect.addSnapshotSerializer(unquoteSerializer)
 
 test('smoke test', async () => {
-  const result = await remark()
+  const processor = remark()
     .use(remarkEmbedder, {
       transformers: [CodeSandboxTransformer],
     })
+    // @ts-expect-error - Type inference issue with remark plugins
     .use(remarkHTML, {sanitize: false})
-    .process(
+  
+  const result = await processor.process(
       `
 This is a CodeSandbox:
 

src/index.ts

@@ -1,4 +1,4 @@
-import type {Transformer} from '@remark-embedder/core'
+import {type Transformer} from '@remark-embedder/core'
 
 const transformer: Transformer = {
   getHTML: urlString => {