Return Near U128 instead of primitive u128

[bh2smith]

The current return value here is coming back as number type in scientific notation 5e22. I believe if you used U128 wrapper from near_sdk that this value would be serialized to a lossless string instead.

mpc/chain-signatures/contract/src/lib.rs

Line 220 in 568fb11

pub fn experimental_signature_deposit(&self) -> u128 {

This was discovered while implementing dynamic deposit here:

BitteProtocol/near-ca#99

[volovyks]

Thank you @bh2smith , good point.