Improve markdown serialization to minimize failures at build time

[arabello]

Consequence of #44

List of failing packages based on this run gathered from logs:

❯ cat ~/Downloads/job-logs.txt | grep "Failed to serialize readme for package"
2024-09-08T18:13:18.9446312Z       Failed to serialize readme for package "discord-snippet@0.1.1":
2024-09-08T18:13:20.0464722Z       Failed to serialize readme for package "better-typography@0.1.3":
2024-09-08T18:13:20.9982293Z       Failed to serialize readme for package "vim-digraphs@0.1.0":
2024-09-08T18:13:25.6590971Z       Failed to serialize readme for package "espanso-pinyin-tones@0.1.0":
2024-09-08T18:13:25.7665618Z       Failed to serialize readme for package "arrows@0.1.0":
2024-09-08T18:13:26.2200906Z       Failed to serialize readme for package "portuguese-accents@0.1.0":
2024-09-08T18:13:27.9621323Z       Failed to serialize readme for package "flutter-snippets@0.1.0":
2024-09-08T18:13:28.4197001Z       Failed to serialize readme for package "alt-codes@0.1.0":
2024-09-08T18:13:31.0977712Z       Failed to serialize readme for package "med-expansions@0.1.0":
2024-09-08T18:13:31.6461945Z       Failed to serialize readme for package "tholzschuh-maths@0.1.0":
2024-09-08T18:13:32.0159133Z       Failed to serialize readme for package "discord-snippet@0.1.1":
2024-09-08T18:13:32.2656972Z       Failed to serialize readme for package "better-typography@0.1.3":
2024-09-08T18:13:32.7877218Z       Failed to serialize readme for package "vim-digraphs@0.1.0":
2024-09-08T18:13:35.6468150Z       Failed to serialize readme for package "arrows@0.1.0":
2024-09-08T18:13:35.6700644Z       Failed to serialize readme for package "espanso-pinyin-tones@0.1.0":
2024-09-08T18:13:35.9449870Z       Failed to serialize readme for package "portuguese-accents@0.1.0":
2024-09-08T18:13:36.2787264Z       Failed to serialize readme for package "calc-macos@0.1.0":
2024-09-08T18:13:36.8225694Z       Failed to serialize readme for package "flutter-snippets@0.1.0":
2024-09-08T18:13:37.0751900Z       Failed to serialize readme for package "alt-codes@0.1.0":
2024-09-08T18:13:38.5126181Z       Failed to serialize readme for package "med-expansions@0.1.0":
2024-09-08T18:13:39.2526048Z       Failed to serialize readme for package "tholzschuh-maths@0.1.0":

job-logs-failures-mdx.txt