Memory leak in C guests

I think copilot comments about leaks are technically correct, although they are not introduced by this PR. This code has been moved so they appear as added. I would prefer fixing it in a separate PR: expose paired `dealloc` function so that c users don't use `free()` for rust allocated content.

_Originally posted by @andreiltd in https://github.com/hyperlight-dev/hyperlight/issues/1792#issuecomment-5542202312_

The issue identifies the C guest interface and Rust-allocated content as the starting area, but names no files or tests. Trace where C callers currently use free() and where the corresponding Rust allocation is exposed; done means a paired dealloc function is available to C users and its behavior is covered by tests.

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