Fix variable size bytes output for operator id fn

[vanderian]

Motivation

current impl of GetOperatorID() uses big.Int.Bytes() fn which is not fixed in size
for values such as:

g1.x = 5057380699593752404133723351400442269436321976269356819697538492070112962825
g1.y = 63181752827174633838690742712527804366333094176439493577707800024549061549

g1.x.Bytes() = 0x0b2e6043f9172f0910023e406597d9c42571c7b810c35052c896ddaaee96a909
g1.y.Bytes() = 0x23c27576442b69b7d8497b55ced346743564d58ef3e070578ed99d64c673ad
id = 0x62abc5097efdd84a760cc6b55661f858379fe409aecd9e50e9dc92b22af5c0a0

the g1.y.Bytes() is not [32]byte sized and produces an invalid pubkey hash

Solution

using the FillBytes(new([32]byte)[:]) we use proper fixed sized byte arrays to produce the hash

g1.x.Bytes() = 0x0b2e6043f9172f0910023e406597d9c42571c7b810c35052c896ddaaee96a909
g1.y.Bytes() = 0x0023c27576442b69b7d8497b55ced346743564d58ef3e070578ed99d64c673ad
id = 0x011f431d33c8ac9df5f8b5aab5d52747bcbd268c11bd4403042d216757f8959c

[samlaf]

Thanks for this! Just checked and seems like eigenDA fixed this bug in their codebase.
But they used geth's U256Bytes function: https://github.com/Layr-Labs/eigenda/blob/3c66c994e6ffb09afcf957b68fe6e01d34d614bf/core/attestation.go#L103C48-L103C65
Tested and those 2 functions give the same result for your case, but are we confident the simple Bytes conversion always gives the correct result? I feel like I'd rather use geth's U256Bytes to make sure we're exactly equivalent to whatever the evm is doing.

[samlaf]

Fixed in #151 , closing here.