test: Add tests for `const fn` #821

Job	Run time
Benchmark	1m 36s
Check (x86_64-unknown-linux-gnu, 1.67.0)	16s
Documentation	10s
Check (x86_64-unknown-linux-gnu, stable)	15s
Clippy	14s
Check (aarch64-apple-darwin, 1.67.0)	29s
Rustfmt	6s
Check (aarch64-apple-darwin, stable)	14s
Test (x86_64-unknown-linux-gnu, 1.74.0)	1m 17s
Check (x86_64-pc-windows-msvc, 1.67.0)	38s
Test (x86_64-unknown-linux-gnu, stable)	1m 11s
Check (x86_64-pc-windows-msvc, stable)	37s
Test (aarch64-apple-darwin, 1.74.0)	1m 10s
Test (aarch64-apple-darwin, stable)	1m 4s
Test (x86_64-pc-windows-msvc, 1.74.0)	2m 13s
Test (x86_64-pc-windows-msvc, stable)	2m 54s
	14m 24s

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