64 Bit Quaternion Request

[tbg10101]

Currently I need to store 64-bit rotations in a double3 or a custom double-precision quaternion. However, it would be helpful for this library to include a double-precision quaternion to be able to rely on first-party code from Unity.

64-bit quaternions are helpful to remove camera jitter when a camera needs to focus on something far away or when rotating very large objects. This has even been admitted by Unity itself since a talk given by Unity about Cinemachine where camera rotations were stored as a double precision to solve this exact issue.

Please add a double-precision quaternion and the nice extension methods to work with the other types.