half-path-based on binary Merkle tree

[ping-ke]

Issue: https://github.com/QuarkChain/TenGPS-research/issues/13

The half path based format is implemetn at
https://github.com/NethermindEth/nethermind/blob/master/src/Nethermind/Nethermind.Trie/NodeStorage.cs#L37

For state (total 42 byte) 
+--------------+------------------+------------------+--------------+
| section byte | 8 byte from path | path length byte | 32 byte hash |
+--------------+------------------+------------------+--------------+
For storage (total 74 byte)
+--------------+---------------------+------------------+------------------+--------------+
| section byte | 32 byte from address | 8 byte from path | path length byte | 32 byte hash |
+--------------+---------------------+------------------+------------------+--------------+

The section byte is:
- 0 if state and path length is <= 5.
- 1 if state and path length is > 5.
- 2 if storage.

To simplify the implementation, this example only retains three fields:
8 bytes from path, path length in bytes, and 32 bytes hash.

The '8 byte from path' is the first 8 bytes of the path
path.Path.BytesAsSpan[..8].CopyTo(pathSpan[1..]);
We use the top depth bits of the key here.