libcovebods: Add handling of BODS 0.4 data

[radix0000]

Include BODS 0.4 schema, update to handle new jsonschema version, include BODS 0.4 specific checks, statistics and tests etc.

[ghost]

If you wanted to split up libcovebods/tasks/checks.py and libcovebods/tasks/statistics.py that would be cool. The files are now so big that GitHub says "Large diffs are not rendered by default." :-) Maybe to keep code changes in this PR readable, changes to existing classes stay in the same file but any new classes could be in new files? Just a suggestion tho, as I realise this may be more work for what is just code neatness.
Tho maybe that would end up with checks for the same thing in different versions in different files, which might not be great?

[ghost]

Is libcovebods/tasks/peps.py ok without a change? (but maybe that can be another PR!)

[ghost]

So libcovebods/data/schema-0-4-0.json is a dereferenced version of the schema, but it wasn't generated by the method described in https://github.com/openownership/lib-cove-bods?tab=readme-ov-file#updating-schema-files-in-data ? Could we just have a note saying this in readme?

I don't think we need to explain fully how it's generated at this time, as maybe we are about to fix compiletojsonschema so it can do so? Or if not we can update the readme later.

[radix0000]

Have broken up checks and statistics, also added some more statistics, a few more tests etc. The schema-0-4-0.json file was added as a test at some point but isn't used, and has been removed.