feat: Expose private class hashing functionality

[t00ts]

Recently, a request was brought up for having our hashing functionality publicly accessible.

Goal is to expose this functionality in a way where it is:

• Publicly accessible (published on crates.io)
• Future-proof (versioned)
• Ergonomic for 3rd-party use (public API with proper docs)

See also:
#2465

[notlesh]

Thanks for taking a look! I'm happy to come up with a cleaner solution than what #2465 proposed.

Just to be clear (esp. since the diff is a bit difficult to look at), what we need in SNOS is a small subset of the existing fn compute_cairo_class_hash().

SNOS uses it here and this value is inserted directly into the VM.

This corresponds roughly to the OS code here and here.