feat(balance): adjust spawns in collapsed sheds

[chaosvolt]

Purpose of change

Lil rebalance per feedback from RoyalFox on the discord, as it turns out the balance of abandoned sheds can get a bit wacky, especially so when you bump item spawn rate up (though that) due to how common full stacks of nails can be in it.

Describe the solution

1. Per feedback, axed the system of having items spawn per tile since the basic floor calls so damn many of them.
2. Instead, placed a few area spawns in a random space within the room. Uses stash_wood and recycle_iron instead of wood_workshop since the latter has more interesting spawns plus is one of the few itemgroups that doesn't spawn entire stacks of nails when it shows up, also replaces the potential calls to mischw with one potential call to tools_carpentry.

Describe alternatives you've considered

Defining a custom group for shed contents.

Testing

1. Checked affected file for syntax and lint errors.
2. Spawned in and poked through a shed after finding one, observed result of clearing the rubble plus whatever spawned on the floor.

Additional context

Checklist

[RoyalFox2140]

Well as long as you're okay with sheds having a low chance of spawning full toolboxes now. The spread of tool spawns makes it worthwhile to investigate and the nails being brought away from counts of 2000 is better

[chaosvolt]

Why is balance always hard...