Research variable length encoding of CIS-2 token amounts

[limemloh]

Tokens standards on Ethereum uses an unsigned 256 integer to represent token amounts, which might cause issues with CIS2's choice of using u64 when application across bridges.

We should reseach the implications of using a variable length encoding such as LEB128 for token amounts in order to support large token amounts while still keeping the option to use a smaller type for the smart contract implementation.

We do this by implementing LEB128 for serializing token amounts in one of the examples and observe the difference in energy cost for interaction and smart contract module size.

[limemloh]

I have implemented a token amount of u64 using LEB128 for serializing and deserializing and compared it to the current implementation, which is using the serialization and deserialization of u64.

On testnet I deployed the wCCD example with LEB128 and with u64 for token amount. I then initialized each contract, wrapped 10 CCD, transferred 10 wrapped microCCD, unwrapped 10 microCCD while recording the costs.

Both contracts are build with no-std, embedded schema using:

• cargo-concordium 2.0.1
• Rustc nightly-2021-06-09-x86_64-unknown-linux-gnu

Contract	Module Size	Deploy	Init	wrap 10	transfer 10	unwrap 10
Fixed u64	48759 B	53796 NRG	1945 NRG	1890 NRG	2156 NRG	2185 NRG
LEB amount u64	49781 B	54919 NRG	1956 NRG	1903 NRG	2162 NRG	2194 NRG

[limemloh]

From the above results we have concluded to use LEB128 encoding of token amount in CIS2