Rewrite how we do inventory transfers

- Add a new ContainerTransfer class to handle moving items between
   containers. This is now used for turtle.drop/turtle.suck as well as
   inventory methods.

 - Any other usages of IItemHandler (which are mostly on turtle
   inventories) now use Container and a couple of helper methods.

buildSrc/src/main/kotlin/cc-tweaked.gametest.gradle.kts

@@ -1,5 +1,3 @@
-import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
-
 /**
  * Sets up the configurations for writing game tests.
  *
@@ -47,7 +45,5 @@ java.registerFeature("testFixtures") {
 
 dependencies {
     add(testFixtures.implementationConfigurationName, main.output)
-
     testImplementation(testFixtures(project))
-    add(testMod.implementationConfigurationName, testFixtures(project))
 }