fix: use helper to deserialize mainnet TTD

[Rjected]

Followup to #5290, using behavior from gakonst/ethers-rs#2617 instead of find/replace to deserialize the mainnet TTD.

[mattsse]

hmm, this is now baked into the jsonu256 helper type, but we only need this for genesis, right?

I think we should instead use an annotation there

[Rjected]

hmm, this is now baked into the jsonu256 helper type, but we only need this for genesis, right?

I think we should instead use an annotation there

ah right, yeah, an annotation would be better so we can just do this hack for TTD rather than for everything

[mattsse]

@Rjected test fails in CI for some reason, couldn't reproduce locally in reth-rpc-types

[Rjected]

hmm, I'm only able to repro with nextest run on the entire repo, but at least I can repro

[Rjected]

hmm, apparently it's possible for is_f64, is_u64, is_i64 to all return false:

running 1 test
val: Number(58750000000000000000000), u64: false, f64: false, i64: false
test serde_helpers::json_u256::test::deserialize_ttd ... FAILED

Should be able to fix though

[Rjected]

@mattsse we can actually use as_str from Number, and pass that into U256::from_str_radix

[Rjected]

nevermind, that's only for arbitrary precision