Parsing of Pb_options according to protobuf schema

[Lupus]

No description provided.

[Lupus]

@c-cube could you please take a look? This is required for further upstreaming of validation generator.

[c-cube]

I can look, but I've also been slowly trying to fix integration tests on master (which were silently broken). Would you look at #243 in the mean time?

[c-cube]

Right now, on my branch (and on this rebased on my branch) dune build src/tests/integration-tests/test_make.ml fails, and I bisected it back to either:

• 8c3dbd5
• b1002fe

which might have broken packed repeated fields? :/

[Lupus]

Right now, on my branch (and on this rebased on my branch) dune build src/tests/integration-tests/test_make.ml fails, and I bisected it back to either:

• 8c3dbd5
• b1002fe

which might have broken packed repeated fields? :/

Yeah, something is wrong, I've got a repro, looking into this.

[c-cube]

merged #243 which conflicts with this, but we're close, I think :).

[Lupus]

Okay, I think I fixed it. This PR includes a small unrelated commit that forces compilation of option_processing.proto, and a fix to duplicate id fields in that file... I hope it's fine to have this extra commit on this PR :)

[c-cube]

It's great! Look at that, it even passes integration tests 😁 .