feat: hide sensitive columns in SnowflakeCompare

[sh13m]

Ported over sensitive column hiding to SnowflakeCompare.

• Moved some methods over into BaseCompare to be synced with PolarsCompare PR (possibly subject to change).
• Added unit tests.
• cast_column_names_lower is not a supported class attribute, and instead the dataframe column names are cast to uppercase to be case-insensitive in _validate_dataframe.
  • sensitive columns setting and validation intent is modified to match this behaviour along with the unit tests.