Uniqueify keys, take two

[radar]

This is a follow-up to #8. I came back to my project today and discovered that dry-equalizer 0.2.1 does not fix this issue for my project, but seemingly fixes at least one case because the tests pass.

So here's a different approach which makes all the tests pass and fixes the issue in my project.

I have absolutely no idea whatsoever why this code is functionally different to what I had before, but there you go. Possibly a Ruby idiosyncrasy?

[radar]

This is still broken in my app:

Without either #8 or this PR:

#<Projects::Project id=1 name="Exploding Rails" tickets=[#<Projects::Ticket title="First errata" comment="I found a boog" project_id=1 user_id=nil id=1 title="First errata" comment="I found a boog" project_id=1 user_id=nil>]>

With this PR:

#<Projects::Project>

I just don't get it.

[flash-gordon]

rom-rb/rom#491 tl;dr mutation is bad, mkay?