Re-organize lp.rs into directory.

[sentilesdal]

Description

Re-organizes lp.rs into a directory structure to match long and short.

Before:

lp.rs // has everything

After:

lp.rs			// just module exports
lp/
  add.rs		// add functionality of HyperdriveLP.sol
  remove.rs		// remove functionality of HyperdriveLP.sol
  math.rs		// LPMath.sol

base.rs			// HyperdriveBase.sol

Review Checklists

Please check each item before approving the pull request. While going
through the checklist, it is recommended to leave comments on items that are
referenced in the checklist to make sure that they are reviewed.

• Testing
  • Are there new or updated unit or integration tests?
  • Do the tests cover the happy paths?
  • Do the tests cover the unhappy paths?
  • Are there an adequate number of fuzz tests to ensure that we are
    covering the full input space?
  • If matching Solidity behavior, are there differential fuzz tests that
    ensure that Rust matches Solidity?

[ryangoree]

nice 🚀

[ryangoree]

placeholder?

[sentilesdal]

yeah, to be filled in shortly