Migrate to `safer_owning_ref`

[noamtashma]

After the maintainer of owning_ref has been unresponsive for a long time, I published my fix of owning_ref known soundness issues as a new crate, safer_owning_ref.

Please migrate to safer_owning_ref.

[bjorn3]

parking_lot doesn't use owning_ref itself. It only has an optional dependency to allow implementing the StableAddress trait of it for the mutex types in case the user wants to use owning_ref. Migrating would break everyone who uses owning_ref with parking_lot mutexes. Having both as optional dependencies would be a possibility though, but I personally don't think safer_owning_ref is nearly as popular for parking_lot to depend on it rather than the other way around. There are several owning_ref alternatives which are way more popular and still maintained like ouroboros and self_cell.

Disclaimer: I'm not a maintainer of this crate.

[noamtashma]

I see. makes sense