upgrade PackTest workflow to simpler + faster version (#56)

- see: https://discord.com/channels/154777837382008833/1185733502294044802/1190466881488945162

.github/workflows/datapack.yml

@@ -2,14 +2,34 @@ name: datapack
 
 on: [push]
 
+env:
+  FABRIC_API: https://cdn.modrinth.com/data/P7dR8mSH/versions/JMCwDuki/fabric-api-0.92.0%2B1.20.4.jar
+  FABRIC_SERVER: https://meta.fabricmc.net/v2/versions/loader/1.20.4/0.15.3/0.11.2/server/jar
+  PACKTEST: https://cdn.modrinth.com/data/XsKUhp45/versions/Gq3rUEy6/packtest-1.3-mc1.20.4.jar
+
 # TODO(37): add linting
 jobs:
   test:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Run PackTest
-        uses: CarbonSmasher/packtest_runner@86d606f25d2bd2faa08b017326fe99964ac3aa5c
+      - uses: actions/setup-java@v4
         with:
-          packs: 'datapacks/omega-flowey'
-          packtest-url: 'https://github.com/misode/packtest/releases/download/v1.0/packtest-1.0-mc1.20.4.jar'
+          distribution: 'temurin'
+          java-version: '17'
+
+      - name: Download server files
+        run: |
+          curl -o server.jar $FABRIC_SERVER
+          mkdir mods
+          curl -o mods/fabric-api.jar $FABRIC_API
+          curl -o mods/packtest.jar $PACKTEST
+
+      - name: Copy packs to world
+        run: |
+          mkdir -p world/datapacks
+          cp -r datapacks world/datapacks
+
+      - name: Run test server
+        run: |
+          java -Xmx2G -Dpacktest.auto -jar server.jar nogui