Fix boolean casting consistency with Pandas (#20746)

[aryansri05]

Description

Closes #20746.

This PR fixes an inconsistency between cuDF and Pandas when casting floating-point columns containing NaN values to boolean while mode.pandas_compatible is enabled.

The Issue:

• Pandas: bool(float('nan')) evaluates to True. Casting a Series [1.0, NaN] to bool results in [True, True].
• cuDF: Previously, NaN values in float columns were treated as nulls, which propagated as nulls after casting to bool ([True, <NA>]).

The Fix:
Updated as_numerical_column in numerical.py. When mode.pandas_compatible is on, if we detect a cast from Float -> Bool on a column with nulls, we explicitly fill the nulls with np.nan before casting. This ensures the underlying cast logic evaluates them as True, matching Pandas behavior.

Checklist

• I am adding a new test (see tests/test_issue_20746.py)
• I have signed off my commits

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