Refactor DefaultNumericTypes into submodule (#181) #407

Job	Run time
Rust format	5s
Rust check	13s
Rust check (--all-features)	17s
Rust check and lint benchmarks	14s
Rust lint	19s
Check sync readme	6s
Rust lint (stable)	10s
Check CLI	13s
Rust check (macOS-latest)	28s
Rust lint (beta)	14s
Rust check (windows-latest)	36s
Rust doc	12s
Rust test	24s
Rust lint (nightly)	18s
Coverage	1m 45s
	5m 34s

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