Remove needless clones and reborrows.

[kivikakk]

No description provided.

[github-actions]

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
./bench.sh ./comrak-17c7cf5	106.6 ± 1.4	104.0	109.9	1.84 ± 0.04
./bench.sh ./comrak-main	108.8 ± 1.2	106.2	111.1	1.88 ± 0.03
./bench.sh ./pulldown-cmark	58.0 ± 0.9	57.2	61.0	1.00
./bench.sh ./cmark-gfm	87.6 ± 8.0	81.1	108.0	1.51 ± 0.14
./bench.sh ./markdown-it	259.8 ± 2.5	253.4	264.3	4.48 ± 0.08

Run on Sun Oct 19 11:02:17 UTC 2025