fix: hydrogen sacs can stack, obsolete endochitin

[chaosvolt]

Purpose of change

A while back I ran into an error with endochitin complaining about not being able to have charges, and haven't seen it trigger any since then, presumably due to #4707 making them stackable.

Now there's still one more non-stacking tissue item obtained by harvesting, so I'm thinking this should fix the associated bug but can't 100% confirm since I can't find a reliable way to force the bug to trigger in the first place.

Relevant issue: #4730

Along the way, in the BN server I was encouraged to obsolete endochitin as it really does nothing for us except flavor.

Describe the solution

1. Added stackable to hydrogen sacs.
2. Migrated out endochitin into regular chitin pieces, since it's basically just chitin pieces except they grow in the body too.
3. Removed endochitin from harvest entries. In return, chitin pieces all got their mass ratio bumped up a bit for any harvest entry that previously had endochitin.

I went ahead and kept hydrogen sacs for now since we might want to mainline hydrogen stuff from Cata++ anyway.

Describe alternatives you've considered

Obsoleting hydrogen sacs for being pointless flavor too. Hydrogen sacs have a use in Cata++ since hydrogen is craftable and used for stuff in it, but that's a third-party mod, and endochitin is still just outright useless.

Testing

1. Checked affected file for syntax and lint errors.
2. Load-tested in compiled test build.
3. Spawned in a giant wasp queen, debug killed it and dissected corpse.
4. Gas sacs show as stacking now.

I tried to mess around with hydrogen sacs before implementing this to see if there was a reliable way of triggering the error but couldn't find a way to force it to trigger the error message.

The old sacs from before I implemented it instead like to do this silliness once converted to stack:

Additional context

Checklist