Threedi-modelchecker

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- Order exported schematisation checks rst table to prevent unnecessarily large git diffs in threedi-docs.
To facilitate this, sets of strings in error messages have been converted to lists of strings.

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- Use Type instead of type so the library works on Python 3.8.

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- Add warning check 208 to check if a(n) (impervious) surface's geometrical area
differs by more than 1 m2 from its defined area

- Add info check 57 to check if pipes and culverts have closed cross-sections.

- Fix check 325; it was giving a warning whenever an interception_file was used.

- Add info check 802 for grid refinement levels equal to kmax.

- Add warning check 615 to check if a surface map references an invalid surface.

- Add error check 1405 to make sure that a DEM does not have more than 5e9 pixels.

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- Unmark checks 26, 27, 28 and 29 as beta.

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- Support marking checks as beta, so they will only be executed with allow_beta_features=True

- Add beta check 26 to make sure friction types with conveyance are only used on v2_cross_section_location

- Add beta check 27 to make sure friction types with conveyance are only used on tabulated rectangle,
tabulated trapezium, or tabulated yz shapes.

- Add beta check 28 to make sure cross-sections with conveyance friction monotonically increase in width

- Add beta check 29 to advise users to use friction with conveyance on cross-sections where it is possible,
but they haven't done so.

- Ignore TypeError raised on check 797 when grid_space is null.

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- Fixed check 204; it now only applies to broad crested weirs/orifices.