Make clvm_rs a replacement for clvm

[richardkiss]

This draws a lot of ideas from various places. Here are the key points:

• the CLVMStorage protocol is fundamental. It has two attributes: atom and the property pair, which is an implicit method call
• Program is the high level wrapper around the low level protocol CLVMStorage. All API is here
• there are only two public exports: Program and EvalError (from clvm_rs import Program, EvalError). Users shouldn't need any others
• run is only supported via rust, and returns a LazyNode which conforms to CLVMStorage (and is generally wrapped by Program)
• sha256tree values are cached when possible all through the tree
• SerializedProgram is no longer needed as CLVMTree replaces it

CLVMTree is great. Here's why:

1. parses quickly in rust and returns pointers to the parsed blob to use as the storage for the atom
2. calculates sha256tree values (optionally, but by default) on parse, for the whole tree
3. caches serialized representations on parse, for the whole tree
4. ideal for use with MOD templates, as curry will be fast, hashing will be fast, and deserialization will be fast
5. maintains these benefits when wrapped by Program

[richardkiss]

I still need to figure out what to do about this.

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