chore: move to iterators

[benfdking]

• small removals of to_string where not necessary

[github-actions[bot]]

Benchmark for 1f4c613

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| Test | Base | PR | % | |------|--------------|------------------|---| | DepthMap::from_parent | **142.2±2.32µs** | 147.8±2.30µs | **+3.94%** | | fix_complex_query | 13.0±0.25ms | 12.8±0.28ms | -1.54% | | parse_complex_query | 4.3±0.06µs | 4.3±0.05µs | 0.00% | | parse_expression_recursion | 7.2±0.10µs | 7.2±0.11µs | 0.00% | | parse_simple_query | **1379.1±22.46ns** | 1456.2±35.83ns | **+5.59%** |