[Magiclysm] Flesh pouch is too large for small survivors

### Describe the bug

Flesh pouch is too large for small survivors

### Attach save file

N/A

### Steps to reproduce

1.Summon flesh pouch as a small survivor (Like a goblin)
2.See its too large.
3.Cry in extra encumbrance

### Expected behavior

Flesh pouch not being too large

### Screenshots

_No response_

### Versions and configuration

- OS: Windows
- OS Version: 10.0.26200.8037 (25H2)
- Game Version: cdda-experimental-2026-03-22-1541-dirty [64-bit]
- Graphics Version: Tiles
- Game Language: English [en]
- Mods loaded: [
Dark Days Ahead [dda],
Disable NPC Needs [no_npc_food],
Portal Storms Ignore NPCs [personal_portal_storms],
Magiclysm [magiclysm],
Extra Mutated Scenarios [extra_mut_scens]
]

### Additional context

I tried adding both overisze and undersize to it but that makes it too small for big people. So I dunno if fixing that would require a tag that makes an item always fit or have the spell conjure a different pouch depending on your size (If that is even possible)

Start by reproducing the Magiclysm flesh pouch summon as both a small survivor, such as a goblin, and a larger survivor, then inspect how the pouch's size and encumbrance are determined. Done means the pouch fits small survivors without becoming too small for larger survivors; the issue does not name a file or test to run.

Written by the indexing model from the issue text.