refactor: upgrade to solidity v0.8.12

hardhat.config.ts

@@ -91,7 +91,7 @@ const config: HardhatUserConfig = {
     tests: "./test",
   },
   solidity: {
-    version: "0.8.9",
+    version: "0.8.12",
     settings: {
       metadata: {
         // Not including the metadata hash

yarn.lock

@@ -1590,7 +1590,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"@nomiclabs/hardhat-ethers@npm:^2.0.5":
+"@nomiclabs/hardhat-ethers@npm:^2.0.4":
   version: 2.0.5
   resolution: "@nomiclabs/hardhat-ethers@npm:2.0.5"
   peerDependencies: