[IlyaKhalafi]

Description

This PR fixes generator-based bulk_create field options failing during SQL construction or after .sql(). With this, field names are captured once before validation and reused for previews and execution.

Empty iterators follow the same validation as empty lists.

Motivation and Context

Fixes #2329.

How Has This Been Tested?

make check and 43 focused tests passed. The full SQLite suite passed with 1,986 tests, 149 skips and two expected failures. PostgreSQL and MySQL SQL generation was checked without live databases.

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codspeed]

Merging this PR will not alter performance

1 warning

⚠️ 21 benchmarks are dominated by system calls

System calls cannot be simulated consistently and are left out of the measure. The reported value understates the real cost. Switch to the Walltime instrument to measure them.

Learn more about system calls

See affected benchmarks

✅ 24 untouched benchmarks

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_{Comparing IlyaKhalafi:fix/bulk-create-field-iterators (72c7a54) with develop (abc91d7)}