feat!: drop support for old node versions

[gameroman]

Summary

Files changed

Test plan

Related to source code (for typings update)

Checklist

• Only the lines required for the fix/feature are changed (no formatter sweeps, no drive-by refactors)
• Tests use real fixture round-trip (wb.xlsx.load / writeBuffer), not synthetic model objects, where possible
• Checked open PRs (gh pr list --state open) for conflicting changes to the same files
• (If serialization is touched) Output verified to open in Excel, or soffice --headless round-trip clean
• (If --no-verify was used to bypass the pre-commit hook) Reason explained above
• (If a major dep was bumped) Runtime smoke test described above