fix: Correctly percent-encode addresses in securejoin invite codes

[Hocuri]

This PR fixes how addresses in securejoin invite codes (i.e. QR codes and invite links) are percent-encoded.

Before this PR,

• @ in the addresses was percent-encoded. This makes the invite code harder to read, and is not necessary; at least, every software we tested correctly handled links that contain @ (Signal, WhatsApp, Telegram, Thunderbird, Delta Chat on Android, iOS, and Desktop)
• But, the first address in the r= parameter of a securejoin link was not percent-encoded at all. This was a sneaky bug caused by using the reduce function; I always find it hard to follow code that uses reduce (and similar functions like fold), and apparently others have the same problem since neither @j-g00da nor @link2xt noticed the problem when implementing & reviewing the PR that introduced the bug.

With this PR:

• @ is allowed in addresses in securejoin invite codes
• all addresses are percent-encoded
• reduced is not used anymore

[link2xt]

I always find it hard to follow code that uses reduce

Reduce is sometimes fine, but not for doing something with the arguments at the same time. E.g. if you need to concatenate all the strings (possibly with the separator), or union all the sets or something like this, then fold/reduce is doing the expected thing.