ci: use coursier cache, do not use bloop

.gitlab-ci.yml

@@ -5,6 +5,15 @@ stages:
 
 default:
   image: gumjoe/wacc-ci-scala:slim
+  cache:
+    - key:
+        files:
+          - project.scala
+      paths:
+        - .coursier-cache/
+
+variables:
+  SCALA_CACHE: --cache=.coursier-cache/
 
 check_format:
   stage: check
@@ -29,7 +38,7 @@ compile_jvm:
   stage: compile
   needs: []
   script:
-    - scala compile --platform jvm -Werror .
+    - scala compile -Werror --server=false $SCALA_CACHE .
   artifacts:
     paths:
       - .bsp/
@@ -45,4 +54,4 @@ test_jvm:
   before_script:
     - git clone https://$EXAMPLES_AUTH@gitlab.doc.ic.ac.uk/lab2425_spring/wacc-examples.git
   script:
-    - scala test --platform jvm .
+    - scala test --server=false $SCALA_CACHE .