Add prettier and eslint caching for local dev

[mfedderly]

• Thanks to @smallsaucepan in Speed up development builds and drop tsup #2988 for these changes
• Deliberately not using this in CI. Prettier takes about 30s, may revisit cache rehydration later
• Also cleans up the lint-staged README generation config, which no longer has to worry about .js files

Subsequent eslint/prettier runs are much faster (m4 macbook pro)

% time pnpm lint:prettier
$ prettier --cache --check .
Checking formatting...
All matched files use Prettier code style!
pnpm lint:prettier  14.26s user 1.19s system 141% cpu 10.892 total

% time pnpm lint:prettier
$ prettier --cache --check .
Checking formatting...
All matched files use Prettier code style!
pnpm lint:prettier  1.93s user 0.74s system 134% cpu 1.985 total

% time pnpm lint:eslint
$ eslint --cache packages
pnpm lint:eslint  5.42s user 0.44s system 178% cpu 3.281 total

% time pnpm lint:eslint
$ eslint --cache packages
pnpm lint:eslint  0.83s user 0.18s system 135% cpu 0.743 total