Fix Randomized Starting Items

[jdunn596]

Fixes #2484

Also addresses a bug where "Buy" item events were considered as valid items to be selected. We now exclude those items by filtering the "Shop" type.

Testing

Rolled multiple seeds to ensure the correct ammo amount was added for the affected items and confirmed in-game as well.

[flagrama]

Why is this not the same as non-randomized starting items in the first place? Wouldn't handling this in the Plandomizer.py file like non-randomized starting items make sense too, so someone could turn it off via plando?

[jdunn596]

For turning it on/off yeah maybe? idk

It made sense for us to handle it in ItemPool.py to give easy access to the entire pool for flexibility and versatility regardless of settings. The exclusions were added afterwards for further flexibility