build(deps): bump mem and webpack-stream

Removes [mem](https://github.com/sindresorhus/mem). It's no longer used after updating ancestor dependency [webpack-stream](https://github.com/shama/webpack-stream). These dependencies need to be updated together.


Removes `mem`

Updates `webpack-stream` from 4.0.3 to 7.0.0
- [Release notes](https://github.com/shama/webpack-stream/releases)
- [Commits](shama/webpack-stream@v4.0.3...v7.0.0)

---
updated-dependencies:
- dependency-name: mem
  dependency-type: indirect
- dependency-name: webpack-stream
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>