Spearbit #89: Addressed review feedback from @Saw-mon-and-Natalie (#827)

* Use safe functions more consistently in `calculateNetCurveTradeSafe`

* Fail if `calculateSharesOutGivenBondsInDownSafe` underflows

* Fixed the rust tests

* Improved the system's liveness when the present value can't be computed

* Improved the liveness properties of `removeLiquidity`

* Ignore `calculateLPSharePrice` failures in `removeLiquidity`

* Ensure that the ending indexes are valid in `HyperdriveFactory` getters

* Used unchecked arithmetic in several places

* Made the `LPMath` safer and used unchecked arithmetic

* Use unchecked arithmetic in the rest of the contracts

* Consolidated the derivative functions in the `LPMath` library

* Addressed review feedback from @jrhea

* Simplified the main loop of `calculateDistributeExcessIdle`

* Addressed review feedback from @Saw-mon-and-Natalie

* Addressed review feedback from @Saw-mon-and-Natalie

Author: jalextowle

contracts/src/libraries/LPMath.sol

@@ -749,11 +749,11 @@ library LPMath {
                         return 0;
                     }
 
-                    // If the max bond amount is greater than or equal to the
-                    // net curve trade, then Newton's method has terminated since
+                    // If the max bond amount is less than or equal to the net
+                    // curve trade, then Newton's method has terminated since
                     // proceeding to the next step would result in reaching the
                     // same point.
-                    if (maxBondAmount >= uint256(_params.netCurveTrade)) {
+                    if (maxBondAmount <= uint256(_params.netCurveTrade)) {
                         return shareProceeds;
                     }
                     // Otherwise, we continue to the next iteration of Newton's
@@ -840,15 +840,15 @@ library LPMath {
     ///
     ///      (1) zeta > 0:
     ///
-    ///          y_max_out(dz) = (z - dz) - zeta * ((z - dz) / z) - z_min
+    ///          z_max_out(dz) = ((z - dz) / z) * (z - zeta) - z_min
     ///
     ///          =>
     ///
     ///          PV(dz) = zeta * ((z - dz) / z) + net_f
     ///
     ///      (2) zeta <= 0:
     ///
-    ///          y_max_out(dz) = (z - dz) - z_min
+    ///          z_max_out(dz) = (z - dz) - z_min
     ///
     ///          =>
     ///