Csvw

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- Fixed bug whereby NULL values list-valued fields couldn't be written to sqlite.

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- Fixed bug whereby it was impossible to set `Column.null` to the empty list.
- Dropped py3.7 compatibility.
- Fixed bug whereby decimals were serialised in scientific notation which is
against the spec.
- Add Python 3.12 to tested and supported versions.
- Replace `lazyproperty` with `functools.cached_property`, since we don't support
py < 3.8 anymore.

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- Fixed support for writing tables to zipped files.

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- DB creation will now drop self-referential foreign-keys by default

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- Fixed the ranges of positiveInteger and nonNegativeInteger

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- Support [JSON Schema](https://json-schema.org/) documents as `format`
annotation for datatype `json`.