Use 'import type' for types instead of 'import' (#636)

Co-authored-by: Shiba <44804845+DeepDoge@users.noreply.github.com>

Author: krzkaczor

Diff for: .changeset/lovely-pears-jam.md

@@ -0,0 +1,8 @@
+---
+'@typechain/hardhat': minor
+'@typechain/ethers-v5': minor
+'@typechain/web3-v1': minor
+'typechain': minor
+---
+
+Prefer `import type` in generated files when possible

Diff for: packages/hardhat-test/hardhat.config.ts

@@ -2,7 +2,7 @@
 import '@typechain/hardhat'
 import '@nomiclabs/hardhat-ethers'
 
-import { HardhatUserConfig } from 'hardhat/types'
+import type { HardhatUserConfig } from 'hardhat/types'
 
 const config: HardhatUserConfig = {
   solidity: '0.8.7',