Retire source-text tests

- Delete 22 test classes whose assertions only read production .java text and check call ordering or literal presence
- Remove 77 source-text assertion methods from 34 test classes that keep real behavioural coverage
- Replace the core process-stream source grep with an ASM gate over compiled core classes in CoreProcessStreamPurityGateTest
- Replace the packs-root source grep in PacksFolderContractTest with an ASM call-site gate over compiled core classes
- Replace the IrisData registered-root regex in PackTypeBukkitPurityGateTest with an ASM scan of the registerLoader class constants
- Trim six mixed tests down to their behavioural assertions and drop their source-text tails
- Drop the eight iris.*Source and three iris.moddedCommonSources test system properties now that nothing reads them

adapters/forge/build.gradle

@@ -240,7 +240,6 @@ tasks.named('compileJava', JavaCompile).configure {
 }
 
 tasks.named('test').configure {
-    systemProperty('iris.moddedCommonSources', file('../modded-common/src/main/java').absolutePath)
 }
 
 processResources {