fix: token paymaster decimal bug

[a00012025]

Summary

When I tried the latest TokenPaymaster in sample, I noticed that it only considers the case of token's decimal being 18, which will cause amount calculation error. This PR fixes this issue by querying the token's decimals when calculating the token amount to transfer to/from paymaster

[drortirosh]

are you sure?
we do have tests that work with decimals=8.
If you do think there is a problem, please also try add a test to it as well.

[0xBigBoss]

Funny, I encountered the same thing when adding the TokenPaymaster to https://github.com/0xsend/sendapp. Really racked my head on this one. I believe for the most part all the calculations are correct except for the ones in UniswapHelper. I think it's missing the decimal scaling when converting. I had a similar approach in our version of UniswapHelper. You can see that here,
develop...0xBigBoss:account-abstraction:develop.

I didn't spend too much time looking at fixing the tests, but you can see now that the actualTokenCharge amounts are inline with what they should be.

actualTokenChargeEvents= 1106
actualTokenCharge= 1106
actualTokenChargeEvents= 1106
expectedTokenCharge= 1106842507747897
    1) should be able to sponsor the UserOp while charging correct amount of ERC-20 tokens

If I understand correctly, the decimal for the token in TokenPaymaster.test.ts is 6, which means this transaction would have used $0.001106 as opposed to $1,106,842,507.747897 😅

I re-wrote most of the tests in solidity for those interested. https://github.com/0xsend/sendapp/blob/7fa242d2069dbfa71c475f73020b17f96670a970/packages/contracts/test/TokenPaymaster6.t.sol#L27

[a00012025]

@drortirosh Hi, I've updated the test to reflect my changes and make them pass. I also updated the assertion of charged token price to avoid floating point error. Please help check it, thanks.

[a00012025]

@drortirosh Hi, can you help check this? Thanks

[0xFirekeeper]

+1, had to make same change for usdc with chainlink oracle