staking,curation: gas optimizations

Staking.collect():

- Merge _collect() and collect() to avoid multiple STATICCALL/SLOAD graphToken()
- Pass graphToken in burnTokens function to avoid multiple STATICCALL/SLOAD
- Change Curation.collect() to work as a "transferAndCall" instead of pulling tokens
- Avoid reading STATICCALL/SLOAD staking() multiple times in takeRewards()
- Remove unused onlyCuration() modifier from Managed
- Remove onlyStaking() modifier and use within the respective function to avoid reading staking() multiple times

Reduce the gas cost of calling Staking.collect() about 20%

_getAllocationState():

- Use storage instead of memory to avoid SLOAD all the attributes that could not be used

Claim():

- Remove setting Allocation struct variables to zero as as the struct is not completely cleaned the refund is not happening. By removing the SSTORE we avoid spending about 20000 gas.

Author: abarmat

contracts/curation/Curation.sol

@@ -160,17 +160,16 @@ contract Curation is CurationV1Storage, GraphUpgradeable, ICuration {
 
     /**
      * @dev Assign Graph Tokens collected as curation fees to the curation pool reserve.
+     * This function can only be called by the Staking contract and will do the bookeeping of
+     * transferred tokens into this contract.
      * @param _subgraphDeploymentID SubgraphDeployment where funds should be allocated as reserves
      * @param _tokens Amount of Graph Tokens to add to reserves
      */
-    function collect(bytes32 _subgraphDeploymentID, uint256 _tokens) external override onlyStaking {
-        // Transfer tokens collected from the staking contract to this contract
-        require(
-            graphToken().transferFrom(address(staking()), address(this), _tokens),
-            "Cannot transfer tokens to collect"
-        );
+    function collect(bytes32 _subgraphDeploymentID, uint256 _tokens) external override {
+        // Only Staking contract is authorized as caller
+        require(msg.sender == address(staking()), "Caller must be the staking contract");
 
-        // Collect tokens and assign them to the reserves
+        // Must be curated to accept tokens
         require(
             isCurated(_subgraphDeploymentID),
             "Subgraph deployment must be curated to collect fees"

contracts/discovery/GNS.sol

@@ -163,7 +163,7 @@ contract GNS is GNSV1Storage, GraphUpgradeable, IGNS {
     /**
      * @dev Approve curation contract to pull funds.
      */
-    function approveAll() external override onlyGovernor {
+    function approveAll() external override {
         graphToken().approve(address(curation()), MAX_UINT256);
     }
 

contracts/governance/Managed.sol

@@ -57,16 +57,6 @@ contract Managed {
         _;
     }
 
-    modifier onlyStaking() {
-        require(msg.sender == address(staking()), "Caller must be the staking contract");
-        _;
-    }
-
-    modifier onlyCuration() {
-        require(msg.sender == address(curation()), "Caller must be the curation contract");
-        _;
-    }
-
     /**
      * @dev Initialize the controller
      */

contracts/rewards/RewardsManager.sol

@@ -346,13 +346,17 @@ contract RewardsManager is RewardsManagerV1Storage, GraphUpgradeable, IRewardsMa
 
     /**
      * @dev Pull rewards from the contract for a particular allocation.
-     * This function will mint the necessary tokens to reward based on the inflation calculation
+     * This function can only be called by the Staking contract.
+     * This function will mint the necessary tokens to reward based on the inflation calculation.
      * @param _allocationID Allocation
      * @return Assigned rewards amount
      */
-    function takeRewards(address _allocationID) external override onlyStaking returns (uint256) {
-        IGraphToken graphToken = graphToken();
+    function takeRewards(address _allocationID) external override returns (uint256) {
+        // Only Staking contract is authorized as caller
         IStaking staking = staking();
+        require(msg.sender == address(staking), "Caller must be the staking contract");
+
+        IGraphToken graphToken = graphToken();
         IStaking.Allocation memory alloc = staking.getAllocation(_allocationID);
 
         uint256 accRewardsPerAllocatedToken = onSubgraphAllocationUpdate(