perf: remove fori loop for fits wcs

[beckermr]

This PR removes the fori_loop in the fits wcs.

[codspeed-hq]

CodSpeed Performance Report

Merging #136 will degrade performances by 71.7%

_{Comparing fitswcs-no-loop (b5b520d) with main (2f64269)}

Summary

⚡ 1 improvements
❌ 1 regressions
✅ 25 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	test_benchmark_invert_ab_noraise[compile]	479.1 ms	1,693.1 ms	-71.7%
⚡	test_benchmark_spergel_init[run]	128.2 µs	84.8 µs	+51.21%