fix: prevent potential UB by deriving repr C for union #4296
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Description
Use repr C for
VMFunctionContextto prevent undefined behavior. I believe this union may exhibit UB since it crosses an FFI boundary. Also, I thinkeqandis_nullmay be called on both instances of the union despite the layout not being guaranteed. This is explained further this by this clippy lint so perhaps it's worth configuring it to bedeny.