fix(structured): anonymize columns whose name is not an identifier

[uwezkhan]

Change Description

PandasDataProcessor._process reads each cell with getattr(row, key) while iterating DataFrame.itertuples(). itertuples renames any column whose name is not a valid Python identifier (a space, a hyphen, a leading digit, a keyword) into a positional field like _1, so the lookup raises AttributeError for the very columns that usually hold PII, such as "Full Name" or "e-mail". The mapping comes straight from df.columns via the analysis builder, so StructuredEngine.anonymize hits this on ordinary input.

Before: only columns named as Python identifiers were anonymized; a "Full Name" column aborted the run, and because the frame is mutated column by column, any columns processed earlier were redacted while the failing PII column was left untouched. After: the cell is read by label with data.at[index, key], the same way the result is already written back, so read and write agree and the column name no longer matters. The tradeoff is a per-cell .at lookup in place of a namedtuple field access, negligible next to the operator call already run on every cell.

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