Unique Mode is Very, Very Slow

## Expected Behavior

Unique mode can process at least ~500 QPS, with preference for >2000 QPS.

## Actual Behavior

Unique mode processes ~200 QPS in the optimal case.

## Steps to Reproduce the Problem

1. Press Ctrl-U on the verbose stream.

## Specifications

- Version: Purr: 1.3.0, fzf: 0.40.0 (fb76893), zsh: 5.9
- Platform: 6.3.11-1rodete1-amd64

## Problem

This is a complex problem that has to do with the efficiency of what purr is doing on unique mode. There's a lot of solutions to this problem, but all are more complex than what is currently being done by quite a bit. I need to think about how I can fix this elegantly without compiling anything if possible. Massive multi-threading may be the solution.