contracts: fetch-batches hardhat task

Adds a hardhat task to fetch batches. Logs are written
to stderr so that the stdout can be written to a file
or passed to `jq`.

```bash
export CONTRACTS_TARGET_NETWORK=...
export CONTRACTS_DEPLOYER_KEY=...
export CONTRACTS_RPC_URL=...
npx hardhat fetch-batches --network main --start 14311261
```

.changeset/few-pears-think.md

+---
+'@eth-optimism/contracts': patch
+---
+
+Add a fetch batches hardhat task

packages/contracts/hardhat.config.ts

@@ -20,6 +20,7 @@ import './tasks/validate-address-dictator'
 import './tasks/validate-chugsplash-dictator'
 import './tasks/whitelist'
 import './tasks/withdraw-fees'
+import './tasks/fetch-batches'
 import 'hardhat-gas-reporter'
 import '@primitivefi/hardhat-dodoc'
 import 'hardhat-output-validator'

packages/contracts/tasks/fetch-batches.ts

+import { ethers } from 'ethers'
+import { task } from 'hardhat/config'
+import * as types from 'hardhat/internal/core/params/argumentTypes'
+import { SequencerBatch } from '@eth-optimism/core-utils'
+
+import { names } from '../src/address-names'
+import { getContractFromArtifact } from '../src/deploy-utils'
+
+// Need to export env vars
+// CONTRACTS_TARGET_NETWORK
+// CONTRACTS_DEPLOYER_KEY
+// CONTRACTS_RPC_URL
+task('fetch-batches')
+  .addOptionalParam(
+    'contractsRpcUrl',
+    'Ethereum HTTP Endpoint',
+    process.env.CONTRACTS_RPC_URL || 'http://127.0.0.1:8545',
+    types.string
+  )
+  .addOptionalParam('start', 'Start block height', 0, types.int)
+  .addOptionalParam('end', 'End block height', undefined, types.int)
+  .setAction(async (args, hre) => {
+    const provider = new ethers.providers.StaticJsonRpcProvider(
+      args.contractsRpcUrl
+    )
+
+    let CanonicalTransactionChain = await getContractFromArtifact(
+      hre,
+      names.managed.contracts.CanonicalTransactionChain
+    )
+    CanonicalTransactionChain = CanonicalTransactionChain.connect(provider)
+
+    const start = args.start
+    let end = args.end
+    if (!end) {
+      end = await provider.getBlockNumber()
+    }
+
+    const batches = []
+
+    for (let i = start; i < end; i += 2001) {
+      const tip = Math.min(i + 2000, end)
+      console.error(`Querying events ${i}-${tip}`)
+
+      const events = await CanonicalTransactionChain.queryFilter(
+        CanonicalTransactionChain.filters.SequencerBatchAppended(),
+        i,
+        tip
+      )
+
+      for (const event of events) {
+        const tx = await provider.getTransaction(event.transactionHash)
+        const batch = (SequencerBatch as any).fromHex(tx.data)
+        batches.push(batch.toJSON())
+      }
+    }
+
+    console.log(JSON.stringify(batches, null, 2))
+  })