Fix the bug in `deposit`

[andreivladbrg]

Linked issues

• Closes https://github.com/sablier-labs/flow/issues/148
• Closes https://github.com/sablier-labs/flow/issues/156

Changelog

Src

• Fixes the bug by changing the "amount" paramater in deposit to transferAmount
• Don't allow ERC20 assets with more than 18 decimals
• Add Helpers library
• Move _calculateTransferAmount and _safeAssetDecimals in Helpers
• Add calculateNormalizedAmount function
• Add checkAndCalculateBrokerFee function in Helpers and use it in _depositViaBroker

Test

• Add new constants with 6 decimals
• Update the tests with the new logic in deposit
• Add more tests in create
• Add more tests in deposit

---

Question: should we add independent tests for Helpers.calculateNormalizedAmount and Helpers.calculateTransferAmount?

[andreivladbrg]

Also, I think we should start using unchecked wherever its safe to do so inspite of it reducing readability. We should save gas on mathematical operations.

I changed my mind, and I added the unchecked blocks in the calculation functions. It wasn’t about readability; rather, I was concerned that something might break, so I thought it was safer not to use unchecked. Also, the gas savings are not high.

[smol-ninja]

Unfortunately, we cannot unchecked the whole block. (amount * (10 ** normalizingFactor)).toUint128() can overflow.

[andreivladbrg]

@smol-ninja updated the PR with not allowing assets with more than 18 decimals