Settle on bigint

[jeluard]

uplc and amaru need to deal with big integer. They both use different crates (num-bigint for amaru and rug for uplc).

It would makes sense to have both aligned, having in mind the following constraints:

• license should be acceptable
• all major OSes should be supported
• performance should be sufficient
• wasm and riscv targets should be supported
• optionally, it should have been audited

rug relies on native dependencies, failing those constraints.

What others node are using

• Aiken uses num-bigint
• Ethrex uses num-bigint
• LightHouse uses num-bigint
• Grandine uses num-bigint
• solana uses num-bigint
• [polkadot-sdk] uses num-bigint
• smoldot (a polkadot light-client) num-bigint

pallas is interesting as it switched between different crates over time. It first considered rug, switched to num-bigint, then to malachite and finally to dashu for licensing reasons.

It looks like the status quo is num-bigint. rug us probably not a great option as it is not well supported on windows and can't compile on wasm/riscv targets.
Performance wise, it looks like dashu is good enough while num-bigint is three times slower (according to those benchmarks)
Both dashu and num-bigint have an acceptable license. Although they don't appear to have been audited.

Lastly, crypto-bigint is an alternative that has been audited, used by risc0

[jeluard]

It could be interesting to have @AndrewWestberg shim in, as I understand he worked on the bigint support for pallas.