* Introduce `--flatten-schema` flag to convert, merge, and split commands.
* Modify database writing functions to support flattened schema names.
* Update template functions to handle schema.table naming convention.
* Enhance PostgreSQL writer to utilize flattened schema in generated SQL.
* Update tests to ensure compatibility with new flattening feature.
* Dependencies updated for improved functionality.
* Implement SanitizeStructTagValue function to clean identifiers for struct tags.
* Update model data generation to use sanitized column names.
* Ensure safe handling of backticks in column names and types across writers.
* Implement SanitizeFilename function to clean identifiers
* Remove quotes, comments, and invalid characters from filenames
* Update filename generation in writers to use sanitized names
