[ChrisW09]

Fixes #549

Problem

docs/core_concepts/config_system.md told readers to pass numerical_method=None to turn off numerical preprocessing. The PreprocessingConfig field table said "Pass None for no transform", and the "Running with no numerical preprocessing" section used numerical_method=None in an example commented # no scaling, binning, or PLE on numeric columns. The boxes below that example built on the same premise. None actually keeps PreTab's default representation (PLE with output_dim columns per feature, unless a preset chooses another). The no-op is the string "none". The PreprocessingConfig docstring was already correct.

Change

Docs only, in docs/core_concepts/config_system.md:

• The field table says None keeps the default ("ple", or the preset's choice) and "none" disables the transform.
• The "Running with no numerical preprocessing" text and example use numerical_method="none", and say explicitly that leaving None keeps PLE unless a preset chooses another representation.
• The important and note boxes refer to "none", and the warning box now explains the difference from the "none" side.

Verification

I ran the updated example against main. With PreprocessingConfig(numerical_method="none", categorical_method=None), the numerical pipeline is imputer -> noop, whereas numerical_method=None gives imputer -> minmax -> ple with width 7. With preset="standard", None resolves to the preset's B-spline representation, hence the preset caveat.

Checks

• just test: 3236 passed, 46 skipped, 28 xfailed; coverage 91.29%
• just docs: build succeeded (warnings treated as errors)
• just check: all hooks passed (ruff, prettier, pyright)