Recover suspend ABI without kotlin.Metadata

[LLeavesG]

Summary

Language selection used only @kotlin.Metadata. R8 often strips that annotation but leaves the DEX SourceFile (.kt), the same attribute JADX uses to recover Kotlin file names. Those classes were decompiled as Java and kept a raw Continuation last parameter.

• treat SourceFile ending in .kt / .kts as Kotlin when metadata is absent
• recover suspend from the JVM shape Object foo(..., Continuation) when the continuation parameter is unused in the body
• skip ContinuationImpl bridges (create, invokeSuspend, and invoke on classes that declare invokeSuspend)

This does not reconstruct switch(label) / COROUTINE_SUSPENDED state-machine bodies. Methods that still pass the continuation through keep the parameter on purpose.

Validation

• cargo fmt --all -- --check
• cargo test -p dexdec --lib (language + ABI unit tests)
• cargo test -p dexdec --test expected_test
• Stripped-metadata sample: 150/150, Java-only → 104 Kotlin files from SourceFile
• Metadata sample: existing suspend kept; one extra unused-continuation emit recovered
• finally / synchronized / goto / brace-balance unchanged vs main

Review notes

Standalone. No overlap with the FunctionN or naming PRs. Merge order is free; the three were also verified stacked together.