Switch from C-style enums to C++ scoped enums

[vyasr]

Description

It would be nice to change all uses of enum in freud to enum class.

Motivation and Context

Scoped enums are generally preferred to C-style enums since they avoid polluting scopes and leaking dependencies, and they do not implicitly convert to integers.

Note that Cython requires 3.0 for full support for scoped enums, but we can still transition our C++ code to use them and then our Cython code will automatically get fixed whenever we updated to 3.0.

[tommy-waltmann]

I think this is worth waiting to address until we require Cython>=3.0 as a dependency. I've played around with this a bit and even just converting the cpp enums requires more work than you'd expect to get the bindings to work properly without cython natively supporting scoped enums.