Consider making Random a weak dep

[jakobnissen]

BioSequences depends on Random, in order to support methods like randdnaseq. Until now, this dependency has been "free", because Random was loaded with Base in the system image, meaning Random was always available.
Starting soon - maybe in Julia 1.11 already, Random will be an external, upgradable package quite similar to ordinary packages. That means it will contribute to latency, and precompilation time. We don't yet know how much latency Random will incur.

We can cut Random as a dependency if we gate methods like shuffle!(::BioSequence) and randseq behind a weak dependency on Random. This will be a breaking change, so let's wait until Random actually is a freestanding stdlib. Nonetheless, I'd support it.

Any opinions? Is this too frivolous a change to release a breaking change?

[kescobo]

Seems fine to me!