Add ERC721 example app

.changeset/short-dingos-sip.md

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+---
+"@ponder/core": patch
+---
+
+Fixed transaction and block formatting to handle Arbitrum RPC data formats.

examples/token-erc721/.env.example

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+# Arbitrum RPC URL used for fetching blockchain data. Alchemy is recommended.
+PONDER_RPC_URL_42161=

examples/token-erc721/.gitignore

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+node_modules/
+.DS_Store
+
+.env.local
+.ponder/
+generated/

examples/token-erc721/README.md

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+# Example ERC721 token API
+
+This example shows how to create a GraphQL API for an ERC721 token using Ponder. It uses the Smol Brains NFT contract on Arbitrum, which emits `Transfer`, `Approval`, and `OwnershipTransferred` events.
+
+## Sample queries
+
+### Get all tokens currently owned by an account
+
+```graphql
+{
+  account(id: "0x2B8E4729672613D69e5006a97dD56A455389FB2b") {
+    id
+    tokens {
+      id
+    }
+  }
+}
+```
+
+### Get the current owner and all transfer events for a token
+
+```graphql
+{
+  token(id: "7777") {
+    owner {
+      id
+    }
+    transferEvents {
+      from
+      to
+      timestamp
+    }
+  }
+}
+```