feat: add walltime benchmark in addition to simulation

[beckermr]

This PR adds a walltime benchmark in addition to the simulation one. It will be more flaky than the simulation one due to the github hosted runners potentially being different machines on the backend each time. That's ok. It is useful to check things in general.

[codspeed-hq]

Merging this PR will improve performance by 34.48%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚡ 1 improved benchmark
✅ 15 untouched benchmarks
🆕 16 new benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	test_benchmarks_lanczos_interp[xval-no_conserve_dc-run]	1,102.6 µs	819.9 µs	+34.48%
🆕	WallTime	test_benchmark_spergel_xvalue[run]	N/A	1.7 s	N/A
🆕	WallTime	test_benchmarks_lanczos_interp[kval-no_conserve_dc-run]	N/A	46.3 µs	N/A
🆕	WallTime	test_benchmark_interpimage_flux_frac[run]	N/A	432.8 µs	N/A
🆕	WallTime	test_benchmarks_lanczos_interp[xval-no_conserve_dc-run]	N/A	88.2 µs	N/A
🆕	WallTime	test_benchmark_spergel_calcfluxrad[run]	N/A	193.3 µs	N/A
🆕	WallTime	test_benchmark_rng_discard[run]	N/A	111.3 µs	N/A
🆕	WallTime	test_benchmark_gaussian_init[run]	N/A	6.3 µs	N/A
🆕	WallTime	test_benchmark_moffat_init[run]	N/A	134.4 µs	N/A
🆕	WallTime	test_benchmarks_lanczos_interp[kval-conserve_dc-run]	N/A	44.1 µs	N/A
🆕	WallTime	test_benchmarks_lanczos_interp[xval-conserve_dc-run]	N/A	120 µs	N/A
🆕	WallTime	test_benchmark_spergel_init[run]	N/A	6.3 µs	N/A
🆕	WallTime	test_benchmark_spergel_conv[run]	N/A	279 ms	N/A
🆕	WallTime	test_benchmark_spergel_kvalue[run]	N/A	11.5 ms	N/A
🆕	WallTime	test_benchmarks_interpolated_image[run]	N/A	5.2 ms	N/A
🆕	WallTime	test_benchmark_invert_ab_noraise[run]	N/A	128.4 µs	N/A
🆕	WallTime	test_benchmarks_metacal[run]	N/A	18.6 ms	N/A

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_{Comparing add-walltime-too (64effd9) with main (e9441e3)}