Remove debug from 'promise-mem'

[gndelia]

debug (and its dependency, ms) take up to 90% of the bundle of the promise-mem package. However,

• The debug info does not really offer too much insight (the key is not even logged)
• The code's been stable for long, so it's rare that we need to debug it
• Ideally, we want to avoid pushing debug in prod.

After discussing with @gabmontes we decided to remove this dependency.

• 7aee109 removes the dep
• 090b98e adds the bundle size badge to the Readme
• 1e3f687 bumps the version

Process checklist

• Manual tests passed or not applicable.
• Automated tests added or not applicable.
• Documentation updated or not required.

Metrics

Actual effort: 0.5h