Disable C version of cbor2 loading

[itamarst]

Fixes https://tahoe-lafs.org/trac/tahoe-lafs/ticket/4088

Update: switched to Rust-based deserialization. I'm hoping to make it run faster, too, in an upcoming release (right now it needs to parse CBOR twice, but that's fixable).

[meejah]

LGTM

[itamarst]

I actually have CBOR deserialization working in Rust, which won't have the downside of being much slower, so maybe I'll update the PR to use that?

[coveralls]

coverage: 94.742%. first build
when pulling f2f7c1d on 4088-disable-c-cbor2
into 2cc9cea on master.

Updated the code

[itamarst]

Apparently pycddl isn't working on PyPy 😢

[itamarst]

Going to have to figure out what's up with PyPy, at first glance it seems like a PyO3 bug, will see.

[meejah]

Obviously we don't want to break PyPy for this, but otherwise looks fine

[itamarst]

PyPy will be fixed with pycddl 0.6.1, hopefully will update PR tomorrow.

[itamarst]

enarx/ciborium#97 implies some potential issues with the underlying Rust CBOR library, but...

1. I can't reproduce any issues with extensive Hypothesis testing (just run 40K examples).
2. We're relying on it for CDDL schema validation, so if it errors on valid CBOR we'd have issues on schema validation too.

So 🤷

[itamarst]

Errors seem... unrelated? Will rerun when final ones finish.

[meejah]

👍