* core/state, light, les: make signature of ContractCode hash-independent
* push current state for feedback
* les: fix unit test
* core, les, light: fix les unittests
* core/state, trie, les, light: fix state iterator
* core, les: address comments
* les: fix lint
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Co-authored-by: Gary Rong <garyrong0905@gmail.com>
The state availability is checked during the creation of a state reader.
- In hash-based database, if the specified root node does not exist on disk disk, then
the state reader won't be created and an error will be returned.
- In path-based database, if the specified state layer is not available, then the
state reader won't be created and an error will be returned.
This change also contains a stricter semantics regarding the `Commit` operation: once it has been performed, the trie is no longer usable, and certain operations will return an error.