Support backref for wasm

[ChiaMineJP]

Added support compressed form of clvm byte representation.

Changed

• Renamed wasm/src/api.rs to wasm/src/run_program.rs
• Added allow_backrefs() method to Flag struct
• run_clvm requires flag argument. If ALLOW_BACKREFS bit is set, it deserializes bytes input of clvm objects as compressed forms.
• When ALLOW_BACKREFS bit is set when calling run_chia_program, it deserializes bytes input of clvm objects as compressed forms.

Added

• Added sexp_from_bytes function.
• Added to_bytes() method to LazyNode

[coveralls-official[bot]]

Pull Request Test Coverage Report for Build 8829620756

Details

• 29 of 79 (36.71%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.4%) to 93.947%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
wasm/src/serialize.rs	0	15	0.0%
wasm/src/lazy_node.rs	0	16	0.0%
wasm/src/run_program.rs	0	19	0.0%
<!--	Total:	29	79	36.71%	-->

Totals
Change from base Build 8310295107:	-0.4%
Covered Lines:	5789
Relevant Lines:	6162

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💛 - Coveralls

[ChiaMineJP]

Consider moving ALLOW_BACKREFS to wasm api, or simply exporting node_to_bytes_backrefs separately.

I'll move ALLOW_BACKREFS to wasm api. In Rust part of clvm_rs, whether to allow backrefs will be decided in the upper scope (like chia_rs). However, in wasm/js part of clvm_rs, developers must tell whether to allow backref or not in the clvm_wasm(clvm_rs)'s scope because from JS world, SExp is always passed as uint8 byte array. So whether the byte stream is compressed or not must be immediately known in run_chia_program or run_clvm and cannot defer.