fix: handle NaN scores in sort_by comparison #68

Job	Run time
Clippy	3m 44s
Check	3m 31s
Test (ubuntu-latest)	5m 30s
Format	8s
Test (macos-latest)	4m 49s
Test (windows-latest)	9m 19s
Build (macos-latest, x86_64-apple-darwin, vgrep)	7m 1s
Build (macos-latest, aarch64-apple-darwin, vgrep)	4m 37s
Build (ubuntu-latest, x86_64-unknown-linux-gnu, vgrep)	4m 52s
Build (windows-latest, x86_64-pc-windows-msvc, vgrep.exe)	9m 53s
	53m 24s

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