next - rename number types

[peterjah]

With the refacto of number serialization, number serializer are exported here
https://github.com/massalabs/massa-web3/blob/next/src/basicElements/serializers/number/index.ts

For each number type, a custom type has been defined, by instance here:

massa-web3/src/basicElements/serializers/number/u128.ts

Line 5 in ddf346e

export type U128 = bigint

Because they have same name, its hard to differenciate them and make it difficult to auto import in vscode.
I propose to rename the types, by instance U128 would be u128T