incorporate method match world age into generated code

[aviatesk]

This implements feedback from the GitHub issue comment at https://github.com/JuliaDebug/CassetteOverlay.jl/pull/66#issuecomment-3524019727.

Specifically, we now use the world age from method matches by directly utilizing Base.Compiler.findall. However, the updated tests pass even without this change, which suggests there may be issues with the test coverage.