[core] Add Entry API for storage2::HashMap (#477)

* [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
16 jobs for master in 10 minutes and 27 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Check
passed #595915
linux-docker
check-std

00:01:32

passed #595916
linux-docker
check-wasm

00:01:57

 
  Workspace
passed #595917
linux-docker
build-std

00:02:01

passed #595918
linux-docker
build-wasm

00:02:45

passed #595921
linux-docker
clippy-std

00:01:43

passed #595922
linux-docker
clippy-wasm

00:01:56

passed #595920
linux-docker
codecov

00:04:02

passed #595923
linux-docker
fmt

00:01:04

passed #595919
linux-docker
test

00:03:09

 
  Examples
passed #595926
linux-docker
examples-clippy-std

00:01:25

passed #595927
linux-docker
examples-clippy-wasm

00:01:12

passed #595928
linux-docker
examples-contract-build

00:03:11

passed #595925
linux-docker
examples-fmt

00:00:16

passed #595929
linux-docker
examples-generate-metadata

00:01:21

passed #595924
linux-docker
examples-test

00:01:41

 
  Publish
passed #595930
linux-docker
publish-docs

00:01:37