* add to workspace
* impl
* include tests for func
* fix broken build
* test passing, found 2 bugs
* add errors package
* added in mockgen
* we check for insertion into the pool based on attester slashings
* test passing
* proper test
* Update beacon-chain/rpc/beacon/slashings.go
* Update beacon-chain/rpc/beacon/slashings_test.go