Fixes an incompatibility caused by click 8.3.0, which passes the default value as-is.

Fixes an incompatibility caused by pyreadstat 1.2.9, which changed original_variable_type from 'NULL' to None

Works around an behavior change in jsonpath-ng 1.8.0 where Child.str gets wrapped in parenthesis.

Fixes tokenization errors when using dask 2024.8.1+. Starting with this
version, dask enforces that tokens remain stable across pickle
round-trips (dask/dask#11320). Capturing self in a lambda fails this
check because instance objects can have non-deterministic pickle
representations. Since calculate_variable_value_length is already a
static method, replacing self with the class name is enough to remove
the capture.

Fixes an import error caused by dask 2024.12.1, which removed the
legacy dask.dataframe.dd submodule (dask/dask#11604). Changes the
import to `import dask.dataframe as dd`, consistent with every other
file in the codebase.

Dask 2025.4.0 optimizes multiple DataFrames together, which exposes
division mismatches when assigning a pandas Series to a dask DataFrame
column. The old reset_index/set_index workaround no longer avoids this.
Replacing it with compute-assign-rewrap via dd.from_pandas, which builds
a clean expression graph. This is safe because __getitem__ already
computes the DataFrame to produce the Series being assigned.

Fixes a unit test to support pandas 2.2.0+. The pandas release fixes a
sorting bug with pandas-dev/pandas#54611. This
commit changes the expected results accordingly.

Also fixes a merge type mismatch introduced by upstream #1709: the
codelist metadata side was cast to StringDtype but the evaluation
dataset side was not. With pandas 2.2.0, empty columns infer as float64,
and merging float64 with string is rejected. Casting both sides to
string before the merge resolves this.