Feature: new ignore operation: LowCardinality(String) vs String

[hh2110]

Summary

• Add support for ignoring LowCardinality differences in column comparisons
• Enhance column equivalence logic to handle IgnoreStringLowCardinalityDifferences flag
• Add comprehensive test coverage for LowCardinality normalization functionality

Co-Authored-By: Claude noreply@anthropic.com

---

Note

Adds IgnoreStringLowCardinalityDifferences to ignore String vs LowCardinality(String) differences in table/column comparisons, with full propagation and tests.

• Diff/Schema Comparison:
  • Add IgnorableOperation::IgnoreStringLowCardinalityDifferences and integrate into normalize_table_for_diff to strip LowCardinality annotations when ignored.
  • Extend compute_table_columns_diff and columns_are_equivalent to accept ignore_ops and normalize columns accordingly.
  • Update ClickHouse diff strategy helpers (nested_are_equivalent, column_types_are_equivalent, json_options_are_equivalent) to accept ignore_low_cardinality and compare types semantically.
• Call Sites:
  • Update usages to pass the new parameter (default &[]) in CLI routines and infra diff utilities (simple_table_diff, lifecycle variants, tests).
• Tests:
  • Add comprehensive tests for LowCardinality-ignore behavior across columns, nested types, JSON typed paths, normalization, and table-level normalization; verify non-LowCardinality differences still detected.

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