Update FeeBankCharger.sol: Refactoring the Modifier

[0xScratch]

Well, this PR is solely based on optimizing some gas by refactoring the modifier to save bytecode size and development cost..

Let's see how
Usually, modifier code is copied in all instances where it is used, thus increasing the bytecode size. By doing a refactor like this and introducing the internal function we can reduce the bytecode size at the cost of one JUMP opcode. Thus, this refactoring might only be used in the scenarios when our modifier is being used more than one time!!

Moreover, I kind of tested this refactor technique and the results were quite appealing, Here they are:

First I created a contract that is same as the one we use commonly (without using any internal function for the modifiers)
and this is the result I get:

quite a basic contract, Ain't it? And then I refactored that modifier with the help of an internal function and gas usage dropped, but with a catch i.e gas usage of each function increased quite a bit (see at the right side of those functions and compare them to the previous one)

That's it. If you found it not worth a change then please let me know. It will be a nice learning process for me then!! 😄

[codecov]

Codecov Report

Patch coverage is 100.00% of modified lines.

Files Changed	Coverage
contracts/FeeBankCharger.sol	100.00%

📢 Thoughts on this report? Let us know!.

[ZumZoom]

Summary:

It saves 800-900 gas on Settlement deploy, however execution cost for FeeBank::deposit* and FeeBank::withdraw* increases by 19. We mostly favour execution gas savings, so we'll leave the code as it is.

[0xScratch]

Yea, that makes sense. Thanks!