[ivorbosloper]

Fixes the converters whose output failed fiboa validate or was incomplete, found when the catalog's single-edition collections were rebuilt.

• DE-MV read one WFS request, and the service caps a request at 20,000 features, so 51,537 of the 71,537 field blocks were missing. It now uses WFSConverterMixin, sorted by fbid so the pages do not overlap. The count request leaves out the output format, which the service rejects with a 500.
• DE-TH writes 0 as area_last_year for a field block that is new this year; that is now empty, and the field no longer required.
• EC-LT, EC-LV and EC-SI declare the crop extension but lacked crop:code, crop:code_list or both. Lithuania's code list is keyed on the group name, so the name is also the code; Slovenia's code is SIFRA_KMRS; EC-SI leaves out the parcels without a crop.
• The conversion tests run the validator without checking its result, so expected_columns now guards these fields.

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[Copilot]

🟢 Approval recommended

No active review issues are recorded for the dataset-converter fixes.

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What changed in this PR

This PR fixes incomplete or invalid output from five dataset converters, improving field coverage and compliance with fiboa schemas.

Changes:

• Pages DE-MV’s WFS requests to retrieve all field blocks.
• Treats missing prior-year area in DE-TH as empty and completes required crop fields for EC-LT, EC-LV, and EC-SI.
• Adds regression checks for WFS pagination and crop-column presence.

File	Description
tests/​test_converter_wfs.py	Checks DE-MV pagination, sorting, and count-request parameters.
tests/​test_convert.py	Requires crop code and code-list columns for the three EuroCrops converters.
fiboa_cli/​datasets/​ec_si.py	Adds crop codes and code-list metadata; excludes parcels without crops.
fiboa_cli/​datasets/​ec_lv.py	Adds crop code-list metadata.
fiboa_cli/​datasets/​ec_lt.py	Uses the crop group name as the crop code.
fiboa_cli/​datasets/​de_th.py	Converts nonpositive prior-year area to empty and makes the field optional.
fiboa_cli/​datasets/​de_mv.py	Uses sorted WFS pagination and omits output format from count requests.
CHANGELOG.md	Documents the converter fixes.

_{Review effort: Balanced}