Draft: Use alloc_mode with uniqueness for block allocations in lambda

[anfelor]

This PR tracks adding the alloc_mode back to lambda, this time with uniqueness information. I have opened it in this repository to make sure we get a clean diff (as the overwriting branch is behind main and we depend on oxcaml#3108).

I am still unsure about some parts of this. In particular:

• Do we need an alloc_mode on lparam.mode and lfunction.ret_mode in lambda.mli?
• Are all of the alloc_heap_aliased and alloc_local_aliased bindings below correct?

[mshinwell]

@anfelor why was this closed - is this change being done elsewhere now?

[anfelor]

@mshinwell Yes, this PR is now at oxcaml#3116; I have already adjusted the link in the wiki.