feat: use assembly in mostSignificantBit

[t4sk]

Rewrite mostSignificantBit using assembly. Code is copied from Uniswap V3 library.

https://github.com/Uniswap/v3-core/blob/05c10bf6d547d6121622ac51c457f93775e1df09/contracts/libraries/TickMath.sol#L66-L107

Quick test on Remix IDE shows that code written in assembly can save up to about 1500 gas

function or assembly?	input	gas
function	max uint	24067 gas
function	0	21948 gas
assembly	max uint	22488 gas
assembly	0	22104 gas

[PaulRBerg]

Hello! This is great, thanks very much for opening a PR.

I apologize for the hassle, but I am on the cusp of releasing PRBMath V3 from the staging branch.

Could I kindly ask you to re-apply your changes onto the tip of the staging branch, and git push with force to your branch?

I would also be happy to do the above myself, but then you wouldn't show up as a contributor anymore.

[t4sk]

sure

[PaulRBerg]

Don't worry, I managed to re-implement this myself. I will close this PR in favor of #135.

I made sure that you remain a git author by modifying the git commit body and referencing you there.