chore(dht): Use `URLSearchParams` to parse search params

[mondoreale]

Summary

I switch to URLSearchParams for query param parsing and kill a dependency (querystring).

URLSearchParams is

• Widely supported by browsers (97%+).
• Available in node (global scope) since v15, stable since v10.

querystring is

• Deprecated.
• Doesn't seem to work well in browsers (breaks browser tests if not treated properly).

Changes

• Ditch querystring
• Use URLSearchParams instead

Limitations and future improvements

• n/a

Checklist before requesting a review

• [x] Is this a breaking change? If it is, be clear in summary.
• [x] Read through code myself one more time.
• [x] Make sure any and all TODO comments left behind are meant to be left in.
• [x] Has reasonable passing test coverage?
• [x] Updated changelog if applicable.
• [x] Updated documentation if applicable.