* [core] Rename Entry to Internal Entry

* [core] Add Entry API for storage2::LazyHashMap

* [core] Add storage2::LazyHashMap::len()

* [core] Migrate tests to use storage2::LazyHashMap::len()

* [core] Implement FromIterator and Extend for storage2::LazyHashMap

* [core] Implement macro to generate LazyHashMap + HashMap Entry API tests

* [core] Remove redundant storage2::HashMap Entry API tests

* [core] Make storage2::HashMap Entry API use storage2::LazyHashMap's Entry API

* [core] Move parameterized Entry API tests into separate file

* [core] Rename InternalEntry to StorageEntry

* [core] Make lazy_hmap module public

* [core] Generate Entry API benches for LazyHashMap and HashMap from macro

* [core] Minor streamlining

* [core] Display hashmap variant in benchmark description

* [core] Fix comment

* [core] Fix typos

* [core] Make more use of BTreeMap Entry API

* [core] Replace unwrap with expect

* [core] Improve comment

* [core] Handle loading from storage

* [core] Restrict unsafe

* [core] Less ops for case "entry not in cache, but in storage"

* [core] Rename len()

* [core] Fix typo

* [core] Fix visibility

* [core] Address comments

* [core] Add test to verify that cache is marked as 'Mutated'

* [core] Shorten code with utility function

* [core] Improve naming

* [core] Add Entry API for storage2::HashMap

* [core] Replace unwrap's with expect's

* [core] Shorten code

* [core] Improve tests

* [core] Improve tests

* [core] Add benches for storage2::HashMap Entry API

* [core] Update comments

* [core] Add + update benches

* [core] Improve benches code, add more benches

* [core] Improve expect messages

* [core] Simplify test structure

* [core] Implement review comments

* [core] Shorten bench code

* [core] Fix bench iterations

* [core] Minimze black_box'es

* [core] Remove code dups

* [core] Shorten code