rename `Encode::to_vec` --> `Encode::pack` ?

[pH14]

This is minor, but one thing I've noticed hopping between language bindings is that all of the various FDB tuple layers use pack and pack_with_versionstamp as the verbs for turning a tuple into bytes, and currently we use to_vec (we don't have a with-versionstamp variant yet). to_vec seems more customary around Rust libs, but I'm wondering if it makes sense to rename for consistency w/ the other FDB bindings, or have both.