* test: getters for Branches
- derive(PartialEq) for Branch
* fix: format code
* test: Slot genesis and add
* fix: change expect message
* test: add ParentMissing error case
- derive(PartialEq) only for tests
* fix: false positive for ParentMissing
* fix: add PartialEq to derive for Branch
* fix: unwrap once only
* fix: simply create an Id
* fix: remove inappropriate meaning
* fix: simplify unwrap for branches.get()