implement () -> () as Runnable downcalls and upcalls (#100)

Author: ktoso

.github/workflows/pull_request.yml

@@ -67,8 +67,7 @@ jobs:
       # run the actual build
       - name: Gradle build
         run: |
-          ./gradlew build -x test --no-daemon # skip tests
-          find .
+          ./gradlew build -x test --no-daemon # just build
           ./gradlew build --info --no-daemon
 
   test-swift:

.gitignore

@@ -32,4 +32,4 @@ Package.resolved
 .gradletasknamecache
 
 # Ignore files generated by jextract, we always can re-generate them
-*/**/*.java
+*/**/src/generated/java/**/*