Reduce explosion airtight cache memory usage (#40912)

Reduce explosion airtight cache memory usage (#40912)

* Reduce explosion airtight cache memory usage

This means you can happily add explosion prototypes again

New approach has the tolerance value data in a shared storage with reference counting.

* Oops fix index removal

* Remove debug code and fix merge conflicts

* Also address my other review

* Oh it's in two places lmao

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Co-authored-by: Princess Cheeseballs <66055347+Pronana@users.noreply.github.com>