Improve precision on pricing model calculation

[estensen]

Testing the pricing model, the price of a preconf at 15M already preconfirmed gas differs slightly from the pricing model article (1.17 GWEI). Investigate if we can improve the precision in the math, maybe by using U256.

bolt/bolt-sidecar/src/state/pricing.rs

Lines 153 to 157 in 8dcd096

	assert!(
	(min_fee_wei as f64 - 1_189_738_950.0).abs() < 1_000.0,
	"Expected ~1,189,738,950 Wei, got {} Wei",
	min_fee_wei
	);

https://research.lido.fi/t/a-pricing-model-for-inclusion-preconfirmations/9136