RPC subcriptions `chainHead_unstable_follow` and `chainHead_unstable_call` never return any notification

[librelois]

I tried to request these 2 new rpc methods based on the documentation in this repository: https://github.com/paritytech/json-rpc-interface-spec

Both methods return a subscription_id, but I never get any notification, the subscription is not closed either, it stays open indefinitely without anything happening.

Also, the spec are not clear on the nature of the value returned by chainHead_unstable_call, nor on the fact that it is a subscription, I have the impression that it is a subscription id on which one will receive the notifications related to this method, if so it should be clarified.

[tomaka]

I've never tried to reproduce this, but I recently wrote a small library based on top of smoldot that uses chainHead_unstable_follow and chainHead_unstable_call and everything seems to be working as intended.