feat(napi/transform): add TransformerOptions::assumptions

[sapphi-red]

so that I can use setPublicClassFields for #6735 when it's ready.

[graphite-app]

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[codspeed-hq]

CodSpeed Performance Report

Merging #7601 will not alter performance

_{Comparing sapphi-red:feat/napi-transform-expose-assumptions-options (4869b59) with main (a07f278)}

Summary

✅ 30 untouched benchmarks