Cache runtime code

[arkpar]

Currently code is hashed with blake2 on every call to runtime, which happens multiple times for each block import/production. Profiling shows it takes a bulk of execution time. Code and version should be cached and cache should be persistent across block states and only updated when code change event is detected.

[bkchr]

I think we can close this?

[arkpar]

Right, state cache also caches storage value hashes.