feat(ro-crate-1.2): introduce validation profile for RO-Crate 1.2

[kikkomep]

This PR introduces an initial implementation of the validation profile compliant with the RO-Crate 1.2 specification, adding support for validating crates that declare this version in their conformsTo property.

The implementation covers the core requirements of the specification, in particular those listed in the quick reference. Any additional rules specific to derived profiles (e.g., Workflow RO-Crate) will be addressed in subsequent PRs, where needed.

How to test

The code is available on the feat/ro-crate-1.2 branch and can be installed as usual via Poetry:

git checkout feat/ro-crate-1.2
poetry install

Development and testing were carried out using the few examples provided by the specification, together with additional ones defined ad hoc and derived from it. These ad hoc examples are located under tests/data/crates/ro-crate-1.2: for each significant requirement (particularly the new ones) in every section of the quick reference, the folder contains a valid crate along with several invalid ones, each designed to exercise a specific violation of that requirement.

CLI options

A few new CLI options have been introduced. In particular, validation now performs additional availability checks on the resources referenced by the RO-Crate. Since these checks require remote connections, they can be disabled via the --skip-availability-check flag:

rocrate-validator validate  --skip-availability-check

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Any kind of feedback (bug reports, misinterpretations of the specs, edge cases we may have missed, etc.) is very welcome and much appreciated 🙂

[related to #107]