Add `"sideEffects": false` to `package.json`

**Is your feature request related to a problem? Please describe.**
Without this field, certain bundlers (namely ESBuild) don't know if they tree-shake this package correctly, so they'll leave it in just in case. In my Remix project, this causes a 1.5MB `node:crypto` polyfill to be included in the bundle for no reason.

**Describe the solution you'd like**
Simply adding `"sideEffects": false` to the `package.json` is enough to fix it. I've tested this with [`patch-package`](https://www.npmjs.com/package/patch-package) and everything works perfectly.

**Describe alternatives you've considered**
N/A

**Additional context**
I'd make a pull-request, but I'd imagine it's easier to have someone on the team do it than to have to do the whole CLA song and dance.