chore: bump river version to v0.210.0 (#346)

## Why

Bump the version of `@replit/river` from 0.209.8 to 0.210.0 to prepare
for a new release.

## What changed

Updated the version number in both the root package definition and the
lockfile entry from 0.209.8 to 0.210.0.

## Versioning

- [ ] Breaking protocol change
- [ ] Breaking ts/js API change

Author: darshkpatel