docs: add natspec to the auctions

src/ConstantVRGEA.sol

@@ -4,10 +4,17 @@ pragma solidity ^0.8.18;
 import {VRGEA} from "src/VRGEA.sol";
 import {unsafeWadDiv} from "solmate/utils/SignedWadMath.sol";
 
+/// @title ConstantVRGEA - Constant Rate Gradual English Auction
+/// @notice This contract extends VRGEA with a constant target sale time for the auction regardless of the amount sold.
 abstract contract ConstantVRGEA is VRGEA {
-    int256 public immutable duration;
+    /// @notice The fixed duration for the auction in dayWads (fixed-point representation of days).
+    int256 public duration;
 
-    /// @dev _duration must be in dayWads
+    /// @dev Initializes a ConstantVRGEA contract with specified parameters.
+    /// @param _startTime The start time of the auction.
+    /// @param _reservePrice The reserve price for the auction.
+    /// @param _minBidIncrease The percentage by which a new bid must exceed the previous bid.
+    /// @param _duration The constant duration of the auction in dayWads.
     constructor(
         uint256 _startTime,
         uint256 _reservePrice,
@@ -17,6 +24,10 @@ abstract contract ConstantVRGEA is VRGEA {
         duration = _duration;
     }
 
+    /// @notice Returns the constant target sale time for the auction.
+    /// @dev Overrides the getTargetSaleTime function from the VRGEA contract to provide a constant target sale time.
+    /// @param numSold The number of items sold, which is not used in this constant implementation.
+    /// @return The constant target sale time for the auction.
     function getTargetSaleTime(int256 /* numSold */) public view virtual override returns (int256) {
         return duration;
     }

src/LinearVRGEA.sol

@@ -1,11 +1,13 @@
-// SPDX-License-Identifier: UNLICENSED
+// SPDX-License-Identifier: MIT
 pragma solidity ^0.8.18;
 
 import {VRGEA} from "src/VRGEA.sol";
 import {unsafeWadDiv} from "solmate/utils/SignedWadMath.sol";
 
+/// @title LinearVRGEA - Linear Variable Rate Gradual English Auction
+/// @notice This contract extends the VRGEA contract with a linear pricing function that defines the rate at which items are available for sale
 abstract contract LinearVRGEA is VRGEA {
-    int256 public immutable perTimeUnit;
+    int256 public perTimeUnit;
 
     constructor(
         uint256 _startTime,
@@ -16,6 +18,10 @@ abstract contract LinearVRGEA is VRGEA {
         perTimeUnit = _perTimeUnit;
     }
 
+    /// @notice Calculates the target sale time based on the amount sold using a linear formula.
+    /// @dev Overrides the getTargetSaleTime function from the VRGEA contract with a linear sale supply schedule.
+    /// @param sold The cumulative amount sold in the auction.
+    /// @return The target sale time based on the linear pricing function.
     function getTargetSaleTime(int256 sold) public view virtual override returns (int256) {
         return unsafeWadDiv(sold, perTimeUnit);
     }