try new jiter LazyIndexMap implementation

[davidhewitt]

Pairs with pydantic/jiter#131

[codspeed-hq]

CodSpeed Performance Report

Merging #1445 will degrade performances by 17.75%

_{Comparing dh/new-jiter (bbbdcbc) with main (ba8eab4)}

Summary

❌ 1 regressions
✅ 154 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	dh/new-jiter	Change
❌	test_dict_of_ints_core_json	1.4 ms	1.7 ms	-17.75%