Remove dependency on `memoffset` when MSRV is bumped to 1.77+

[syberant]

Hi! I'm going down the list of reverse dependencies for memoffset.

core::mem::offset_of was stabilised in 1.77. Your MSRV is now 1.75.

I just wanted to leave a reminder here that you can remove the memoffset dependency whenever MSRV is next bumped (or willing to bump it for this).