Test and fix `math_consts_context!` macro. #388

Job	Run time
Rust format	15s
Rust check	16s
Rust check (--all-features)	13s
Rust check (macOS-latest)	24s
Rust lint	18s
Rust check (windows-latest)	30s
Check sync readme	15s
Rust lint (stable)	22s
Check CLI	21s
Rust lint (beta)	15s
Rust lint (nightly)	19s
Rust check and lint benchmarks	19s
Rust doc	21s
Rust test	20s
Coverage	1m 50s
	6m 18s

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