Do not allow any crowdloan contributions during the VRF period (#3346)

* patch `is_ending` logic for sampling

* Create AuctionStatus abstraction

* clean up apis

* fix docs

* Add check for contributions during vrf

* custom error for this

* fix benchmark

* opening -> starting

* Apply suggestions from code review

Co-authored-by: Kian Paimani <[email protected]>

* Update runtime/common/src/auctions.rs

* avoid divide by zero stuff

Co-authored-by: Kian Paimani <[email protected]>