feat(protocol): LibFixedPointMath contract library license different MAX_EXP_INPUT values

[MarcusWentz]

Motivation

Add license to third party contract library as suggested by @d1onys1us.

Concerns

Expected return types and values seem slightly off.

PRB math exp():
https://github.com/PaulRBerg/prb-math/blob/main/src/sd59x18/Math.sol#L152-L167
type SD59x18 (signed integer) return type seems different than int256 and has

MAX_EXP_INPUT=133084258667509499440;

while our current exp() function supports has

MAX_EXP_INPUT=135305999368893231588;

With

exp(133084258667509499440)

original returns

6277101735386680963982882153334421099665277130643420769258879401421053268429

PRB converted to int256 returns

6277101735386680754977611748738314679353920434623901771623

Should we keep the old fixed point exp() function?
Where do we use exp() math? How critical is exp() resolution? Do we have test edge cases with exp()?

[adaki2004]

@MarcusWentz
I get the point to not use unlicensed files, but first would be free to ask Remco if he would be willing to change the license to MIT - then we do not need to put engineering efforts into it.

This is a critical component (part of 1559 math) and i think would require thorough testing which I do not know we want to go for (?). Since i cannot really estimate the real workload it seems floating point notation differs a little bit, it can be tricky to be tailored. Also would be cool having it as an npm package as well - is it available ?

[adaki2004]

Remco's answer:

You can also find it on my site with an MIT License in the footer.

2π.com/22/exp-ln

I recommed you take it from @transmissions11 Solmate V7 as it's maintained and has test coverage: 

[github.com/transmissions1…](https://github.com/transmissions11/solmate/blob/v7/src/utils/FixedPointMathLib.sol)

[adaki2004]

Compared the expWad() (as Remco suggested) line by line from solmate v7 and only parameters (how to calculate p and q) changed but overall fixed 1e18 size notation and upper/lower limits are the same. Applied those numbers and we are under MIT license now.