Add support for SPDX version 3.1 bindings and update tests

[kartben]

Fixes: #17

I guess this overlaps with #46 but maybe getting this one in first is easier to unlock folks wanting to use 3.1 today.

[bact]

LGTM. Thank you.

Note that as current https://spdx.org/schema/3.1/spdx-json-schema.json still resolve to https://spdx.github.io/spdx-spec/v3.1-RC1/rdf/schema.json, which use https://spdx.github.io/spdx-spec/v3.1-RC1/rdf/spdx-context.jsonld , all the term IRIs in the resolved context will use the outdated https://spdx.org/rdf/3.1/terms/ as base.

Once the URL redirections are updated, we should automatically get the updated base: https://spdx.org/rdf/3/terms/ (3.1 -> 3), at the binding generation time.

(PR #46 get around that URL staleness issue during development cycles by hosting local model artifacts)

[kartben]

@bact / all - what are the next steps to get this merged (and released to pypi)? Thanks!

[bact]

Discussed this together with few other 3.1 related issues on Wednesday's implementers call this week and last week. Basically we don't want to publish anything that is still "under development" without a proper label.

That's why there's an introduction of Ontology.isPreRelease at the binding generator side (shacl2code). That PR JPEWdev/shacl2code#124 has merged already. Once next version of shacl2code is released, we can use it here.

With that information in the binding, any call to the binding will raise FutureWarning.