feat: attempt to add imandra caching

.github/workflows/main.yml

@@ -34,9 +34,32 @@ jobs:
       - name: Build the project
         run: opam exec -- dune build @install
 
+      - name: Restore imandra-tmp opam cache.
+        uses: actions/cache@v2
+        id: imandracache
+        with:
+          path: |
+            /tmp/imandra-tmp/_opam
+          key: ${{ matrix.os }}-imandra-http-api
+
+      - name: Copy Imandra HTTP API 
+        if: steps.imandracache.outputs.cache-hit == 'true'
+        run: 
+          cp /tmp/imandra-tmp/_opam/bin/imandra-http-api /usr/local/bin
+
+      - name: Install Imandra HTTP API (if not available).
+        if: steps.imandracache.outputs.cache-hit != 'true'
+        run: |
+            mkdir -p /tmp/imandra-tmp && cd /tmp/imandra-tmp
+            opam switch create . --empty
+            opam repo add imandra https://github.com/AestheticIntegration/opam-repository.git
+            opam update
+            opam install imandra-http-api
+            cp _opam/bin/imandra-http-api /usr/local/bin/
+            
       # TODO: Reenable this once we figure out how to get imandra server running in the CI. 
-      # - name: Run tests
-      #   run: opam exec -- dune runtest
+      - name: Run tests
+        run: opam exec -- dune runtest
 
       # - name: Upload the build artifact
       #   uses: actions/upload-artifact@v2