chore: enable prettier's cache

[karamaru-alpha]

Summary

Enabled Prettier's cache option to reduce execution time.
The cache file is located at ./node_modules/.cache/prettier/.prettier-cache, and subsequent executions will only target files with modified file hashes.

Before	After(cached)
1.4s $ time npm run format:check > npm run format:check 3.06s user 0.20s system 227% cpu 1.433 total	0.2s $ time npm run format:check > npm run format:check 0.24s user 0.08s system 105% cpu 0.299 total

Appendix

cf. https://prettier.io/docs/cli#--cache