Add a less strict solution representation

[Rigidity]

Rationale

When parsing CLVM solutions currently, the nil terminator is strict since they are represented as a normal list. This is fine if the solution is structured correctly, but as seen in Chia-Network/chia-blockchain#18500, this is not always the case. I had an NFT which failed to parse due to this mistake of including the coin amount in the NFT state layer solution.

How does this fix the issue

Instead of requiring the solution's terminator (which here refers to the last CLVM pair's "rest" value after extracting all of the required values in the list) to be nil, it can be any value and is not checked. This is achieved by adding a new representation solution which is identical to list except with this extra bit of flexibility. When serialized, it still includes the nil terminator as it should.

Side effects

The SingletonSolution type is used in the fast-forward feature, so it's a consideration whether allowing this flexibility makes sense for that mempool logic. If not, a separate StrictSingletonSolution could be created with the representation list, for use cases like that. It's not clear to me whether this is important though.

[coveralls-official]

Pull Request Test Coverage Report for Build 10482486683

Details

• 51 of 52 (98.08%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 83.925%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/clvm-derive/src/parser/attributes.rs	2	3	66.67%

Totals
Change from base Build 10422144649:	0.04%
Covered Lines:	12347
Relevant Lines:	14712

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💛 - Coveralls