resolve

[Dev Deps] update `eslint`, `@ljharb/eslint-config`, `array.prototype.map`, `safe-publish-latest`, `tape`

[actions] reuse common workflows

[Tests] only run `eclint` on intended files

[Refactor] `sync`: Do not throw on missing files in `isFile`/`isDirectory`

[Tests] test node 15, 16 on appveyor