Refactor and enhance query building with new features

- Reorganize query spec tests into descriptive blocks for better clarity
- Simplify SQL output formatting by avoiding unnecessary gsub calls
- Add handling for aggregate functions like COUNT, SUM in the select clause
- Implement BETWEEN condition for more flexible queries
- Refactor find_column method to support table-specific column lookup
- Improve error messages for missing columns
- Update schema to include an orders table with relevant fields
- Minor syntax corrections and code formatting improvements