Add Gen IV Great Marsh changing encounters

[Machine-Maker]

Change description

Closes #1496

• Adds new condition type for great marsh selection, x of 32 options.
• Adds encounters for all the changing pokemon, taking into account pre and post national dex states.

AI coding assistance disclosure

Claude Code helped me analyze decompiled diamond and platinum repos. Also generated the big huge changes based on how they work.

Contributor check list

• I have written a description of the contribution and explained its motivation.
• I have written tests for my code changes (if applicable).
• I have read and understood the AI Assisted Contribution guidelines.
• I will own this change in production, and I am prepared to fix any bugs caused by my code change.

[jemarq04]

I've been taking a look at these but I think before I do an in-depth review I'd like you to manually go through these yourself. From an initial glance, rates seem to be incorrect and I'm already seeing duplicates from my first look at Area 1 (e.g. Wooper).

I've made a couple other comments below.

[Machine-Maker]

It might look like there are duplicates, but that's just cause there are 2 encounter slots for each area. So we need them to be possible on each slot.

Say for diamond, for example. Each of the "special" pokemon, when selected, have a 10% encounter rate in that area. It's the same for every pokemon. But that 10% is distributed across 2 different encounter slots. This is because it decreases the encounter rate for 2 separate pokemon by 5% each (by replacing that slot). So there are a lot of what seem like duplicates, but they are just in different encounter slots.

The same is true for platinum, there are 2 5% "wooper" encounters that are replaced by the 2 5% encounters for the selected pokemon.

For D/P, its either encounter_slot_id 7 or 8

For Plat, its either encounter_slot_id 129 or 130.

[jemarq04]

It might look like there are duplicates, but that's just cause there are 2 encounter slots for each area. So we need them to be possible on each slot.

Say for diamond, for example. Each of the "special" pokemon, when selected, have a 10% encounter rate in that area. It's the same for every pokemon. But that 10% is distributed across 2 different encounter slots. This is because it decreases the encounter rate for 2 separate pokemon by 5% each (by replacing that slot). So there are a lot of what seem like duplicates, but they are just in different encounter slots.

The same is true for platinum, there are 2 5% "wooper" encounters that are replaced by the 2 5% encounters for the selected pokemon.

For D/P, its either encounter_slot_id 7 or 8

For Plat, its either encounter_slot_id 129 or 130.

Ok, thanks for the explanation. I've done a more thorough review and the encounters are looking good - thank you for adding these in! All that's left is to address the previous comments I left. I'll take a look at your other PRs soon as well.

[Naramsim]

Oh no! :((( Merge conflicts :)

sorry guys!

[Machine-Maker]

Ok, fixed conflicts, shifted all the ids down.