Use arbitrary feature instead of cfg fuzzing for conditional compilation

[Rigidity]

The benefits are the following:

• Enables rust-analyzer to enable that code path, allowing for better error reporting instead of being grayed out.
• Disables the arbitrary dependency in production.
• Simplifies some code in the fuzz tests.
• You can use arbitrary in non-fuzz dependents if desired now.

[coveralls-official]

Pull Request Test Coverage Report for Build 8877886551

Details

• 1 of 9 (11.11%) changed or added relevant lines in 5 files are covered.
• 31 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.2%) to 84.867%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/chia-wallet/src/puzzles/nft.rs	0	1	0.0%
crates/chia-protocol/src/bytes.rs	0	2	0.0%
crates/chia-protocol/src/chia_protocol.rs	0	2	0.0%
crates/chia-wallet/src/proof.rs	0	3	0.0%

Files with Coverage Reduction	New Missed Lines	%
crates/chia-bls/src/signature.rs	4	95.97%
crates/chia-bls/src/public_key.rs	4	92.94%
crates/chia-bls/src/secret_key.rs	5	94.74%
crates/chia-protocol/src/program.rs	18	68.56%

Totals
Change from base Build 8847398065:	-0.2%
Covered Lines:	11766
Relevant Lines:	13864

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💛 - Coveralls

[arvidn]

at some point we should document the features we have