Tests for ICS23 membership proofs in evm (#108)

fixes #103, tests are based on the official tests data available at
https://github.com/cosmos/ics23/tree/master/testdata/tendermint

Gas cost is pretty high but there is a lot of room for improvements
(submitted #109):
```
evm-contracts> Running 7 tests for /nix/store/g065da2ff3680jqg3fpcs461hmciwh19-source/tests/src/ICS23.t.sol:ICS23Test
evm-contracts> [PASS] testDecode() (gas: 24241)
evm-contracts> [PASS] testExistLeft() (gas: 275292)
evm-contracts> [PASS] testExistMiddle() (gas: 252194)
evm-contracts> [PASS] testExistRight() (gas: 155647)
evm-contracts> [PASS] testNonExistLeft() (gas: 289332)
evm-contracts> [PASS] testNonExistMiddle() (gas: 561288)
evm-contracts> [PASS] testNonExistRight() (gas: 224928)
```