feat: vm.getWallets() (#620)

Companion PR for foundry-rs/foundry#9052

Adds the cheatcode `function getWallets() external returns (address[]
memory wallets)`

Author: yash-atreya

src/Vm.sol

@@ -13,6 +13,6 @@ contract VmTest is Test {
     }
 
     function test_VmSafeInterfaceId() public pure {
-        assertEq(type(VmSafe).interfaceId, bytes4(0x6beed0a1), "VmSafe");
+        assertEq(type(VmSafe).interfaceId, bytes4(0xb09496a4), "VmSafe");
     }
 }