* PoC

* introduce IdProvider trait

* revert Cow stuff

* Update ws-server/src/server.rs

* fix tests

* cargo fmt

* use 'static lifetime in SubscriptionId

* fix tests

* fmt

* make tests compile again

* fix tests

* Fix tests

* Move IdProvider impls to own module

* move `sub-id gen` types to `core`

* fix doc links

* make rand non-optional dep

* feature gate: id provider

Co-authored-by: David Palm <dvdplm@gmail.com>