Overlay: Make shiny count and target number more consistent

[hanzi]

Description

This handles cases where two Pokémon of the same evo line are available on a route.

Instead of using the target for the entire evo line for both Pokémon, deduct them from each other.

The goal is that the sum of 'shinies obtained' in the route encounters list, as well as the sum of target numbers, will always be the same regardless of which of the two Pokémon has been obtained.

As an example, in the northern area of the Safari Zone it will work as follows with Doduo/Dodrio:

• Start with Doduo 0/1🎯 and Dodrio 0/1🎯
• If two Doduo have been found: Doduo 2/2✅, Dodrio 0✅
• If a Doduo and a Dodrio have been found: Doduo 1/1✅, Dodrio 1/1✅
• If TWO Doduo and ONE Dodrio have been found: Doduo 2/1✅, Dodrio 1/1✅

Now, in the southern area (where only Doduo is available) it will work as follows:

• Start with Doduo 0/2🎯
• If one Doduo has been caught: Doduo 1/2🎯
• If two Doduo have been caught: Doduo 2/2✅
• If NO Doduo has been caught, but a Dodrio had previously been caught: Doduo 0/1🎯
• If a Doduo and a Dodrio have been caught: 1/1 Doduo✅

The last two might be confusing, but I guess they are sort of correct. In both cases, we only need one Doduo.

And a last example with Pikachu, where the pre-evolution is not available on the same route:

• If no Pichu and no Pikachu have been caught: Pikachu 0/2🎯
• If one or two Pikachu have been caught, but no Pichu: Pikachu 1/2🎯 or Pikachu 2/2✅
• If one Pichu has been found but no Pikachu: Pikachu 0/2🎯
• If two Pichu have been found but no Pikachu: Pikachu 0/1🎯
• If three Pichu have been found but no Pikachu: Pikachu will no longer appear as a target.

Checklist

• Black Linter has been ran, using --line-length 120 argument
• Wiki has been updated (if relevant)