Refactor, simplify, speed up.

[kivikakk]

This mostly just applies to smart quotes, which are unlikely to benefit hugely (small String optimisation?), but I'm interested in seeing how far we can go with Cow; what if we can avoid allocations entirely in some cases by referring to the input?

[github-actions]

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
./bench.sh ./comrak-094ddb7	128.6 ± 1.5	126.7	132.9	2.20 ± 0.11
./bench.sh ./comrak-main	128.9 ± 2.6	126.2	139.7	2.21 ± 0.11
./bench.sh ./pulldown-cmark	58.3 ± 2.7	56.8	74.8	1.00
./bench.sh ./cmark-gfm	87.4 ± 7.9	81.3	105.3	1.50 ± 0.15
./bench.sh ./markdown-it	259.5 ± 3.1	254.0	265.1	4.45 ± 0.21

Run on Sat Oct 18 10:30:46 UTC 2025

[kivikakk]

Rewritten an incredible amount of 2018-era C-isms and laid bare the control flow in a bunch of places! Soooo much nicer.