Cleaning up walk_to and related procs

[GDNgit]

Heya, this is a great place to start for new contributors or those who wanna start getting into fixing GC issues. Please read up on this and the DM ref sheet before doing so.

My sweet, sweet GC GBP.

"What's walk_to?"
Walk_to(and related) is a base byond command that handles movement. This is used in many different situations, such as the movement handling for simple_animals and the supermatter crystal.

"What's the issue with walk_to?"
Walk_to has a problem with references, when a walk_to is called, it stores a ref to the mob and makes it move... this ref is never properly cleared.

"The server must be dying right? That's a whole bunch of GC issues!"
Well, no. Walk_to is largely a false positive GC issue, taking only a fraction of a second to clear (most of the time). This makes other GC issues nigh impossible to detect without using a ref finder. The ref finder will also show no refs when walk_to causes a GC fail due to it being a base byond instruction.

"Well, how do we fix it?"
Proc walk_to(src, 0) on the atom being moved destroy(). This clears the walk_to and fixes the GC issue.

Below is a list of files that need to be cleaned up to prevent more GC false positives.

Walk_to

• Spiderlings- Reset spiderling walk instructions on Destroy. #19171
• Simplebots- [GBP NO UPDATE][READY FOR TM] Simplemob GC improvement  #19225
• Simpleanimals- [GBP NO UPDATE][READY FOR TM] Simplemob GC improvement  #19225

Step_to

• Projectiles (May still GC due to different stuff, but it's for the best to test all of these)
• AI terror spiders
• Blood streak decals (Yes this uses step, no it shouldn't fail often, but it likely will rarely)
• Slimes - [GBP NO UPDATE][READY FOR TM] Simplemob GC improvement  #19225 (These are awful and will GC fail all the time due to other refs)
• Ninja martial art (Unused)
• His grace
• Medibots- [GBP NO UPDATE][READY FOR TM] Simplemob GC improvement  #19225
• Simplebots- [GBP NO UPDATE][READY FOR TM] Simplemob GC improvement  #19225

Step_towards

• magnitis
• anomalies
• singularity hammer (This has caused some of the most confusing looking GC issues
• spray cleaners (includes chemsprayer)
• alien hunters (these things fail to GC for other reasons too)
• magnet module
• hallucinations
• disk drive
• extinguishers
• reagent_vortex(blob stuff)
• Nanofrost atmos backpacks
• ENsuperhero suit (just remove superheros, shitty meme)
• floor cluwne- [GBP NO UPDATE][READY FOR TM] Simplemob GC improvement  #19225
• mecha syringe
• more bot stuff- [GBP NO UPDATE][READY FOR TM] Simplemob GC improvement  #19225
• supermatter & singulo - DO NOT ATTEMPT THIS UNLESS YOU KNOW WHAT YOU'RE DOING
• mob stuff - Likely not an actual issue funny enough

Step_away

• More terror spider AI
• Alien larva
• Aliens
• Robots if they are hit with hulk
• Mech gripper
• Mob stuff
• slimes
• blobs
• mecha grabsling
• Slime transformation

Get_step_away

• Adminarts
• Powerfist
• Containment gens
• Blob stuff (Yes, again)
• mjollnir
• Atmos energy axe
• knighthammer (admin only)
• prison cube
• anomalies
• hivelords (unused)
• repulse
• cult airlocks
• VOG
• machine megafauna
• human defense

walk_away

• clusterbombs - Grenade GC improvement #19355
• terror AI
• honktumor (shoes b-gone)
• honk mecha module
• simpleanimals - [GBP NO UPDATE][READY FOR TM] Simplemob GC improvement  #19225

walk_towards

• bupplegum
• space dust
• machine megafauna
• rod

NOT LISTED: Walk() and Step(). Just don't have the time yet.
Please direct yourself to https://github.com/tgstation/tgstation/blob/master/.github/guides/HARDDELETES.md for more info on harddels and walk_to stuff
Please direct yourself to tgstation/tgstation#62567 for information on the subsystem TG uses for these procs instead of the byond built in systems