URI verification

[Luukdegram]

Currently, the URI parser is quite naive.
It does check for correctness in the scheme, and somewhat in the host, and in the port.
However, it does not check for correctness in the path, query, and fragment components and simply uses entire slices without verifying.

Parser must comply with

• https://datatracker.ietf.org/doc/html/rfc3986
• https://gemini.circumlunar.space/docs/specification.html (section 1.2)