Fix: Don't allow a threshold of 0 (#123)

* Pausable: implement Pausable abstract contract

* WormholeEndpointStandalone: add pausing functionality

* Pausable: use custom errors instead of require

* feat: add pausing to WormholeEndpoint, WormholeEndpointAndManager, and WormholeEndpointStandalone

* Pausable: remove superfluous comments

* Pausable: rmv leading underscore on [`isPaused`]

* WormholeEndpointStandalone: rmv outdated doctag

* Pausable: move to libraries

* Endpoint: abstract Pausing functionality out to all endpoints

* EndpointStandalone: expose pausing through the Endpoint Standalone API

* Pausable: add configurable pauser role

* Feat: allow owner or pauser role to pause

* Pausable: fix typo in comment

* fix: modify structure to inherit PausableOwnable to linearize access controls

* fix: make renounce and transfer public

* fix: override transferOwnership in ManagerStandalone

loop through all the endpoints and update the owner of all the endpoints to be the owner of the manager

* fix: define new transferOwnership method instead of initializing

* fix: rmv pass through upgrade from Manager

* fix: use interface for manager instead of manager directly

* Fix: Don't allow a threshold of 0

---------

Co-authored-by: Rahul Maganti <rahulmaganti@rahuls-mbp.mynetworksettings.com>

Author: djb15

src/ManagerStandalone.sol

@@ -78,6 +78,10 @@ contract ManagerStandalone is IManagerStandalone, Manager, Implementation {
     /// =============== GETTERS/SETTERS ========================================
 
     function setThreshold(uint8 threshold) external onlyOwner {
+        if (threshold == 0) {
+            revert ZeroThreshold();
+        }
+
         _Threshold storage _threshold = _getThresholdStorage();
         uint8 oldThreshold = _threshold.num;
 
@@ -110,9 +114,11 @@ contract ManagerStandalone is IManagerStandalone, Manager, Implementation {
         // Instead, we leave it up to the owner to manually update the threshold
         // after some period of time, ideally once all chains have the new Endpoint
         // and transfers that were sent via the old configuration are all complete.
+        // However if the threshold is 0 (the initial case) we do increment to 1.
         if (_threshold.num == 0) {
             _threshold.num = 1;
         }
+
         address[] storage _enabledEndpoints = _getEnabledEndpointsStorage();
 
         emit EndpointAdded(endpoint, _enabledEndpoints.length, _threshold.num);
@@ -221,13 +227,14 @@ contract ManagerStandalone is IManagerStandalone, Manager, Implementation {
     function _checkThresholdInvariants() internal view {
         _Threshold storage _threshold = _getThresholdStorage();
         address[] storage _enabledEndpoints = _getEnabledEndpointsStorage();
+        address[] storage _registeredEndpoints = _getRegisteredEndpointsStorage();
 
         // invariant: threshold <= enabledEndpoints.length
         if (_threshold.num > _enabledEndpoints.length) {
             revert ThresholdTooHigh(_threshold.num, _enabledEndpoints.length);
         }
 
-        if (_enabledEndpoints.length > 0) {
+        if (_registeredEndpoints.length > 0) {
             if (_threshold.num == 0) {
                 revert ZeroThreshold();
             }