fix: Backtesting #1: Event fetcher (Infura → JSON Lines cache) (#315)

Add onchain/script/backtesting/fetch-events.ts — a tsx script that:
- Fetches Swap/Mint/Burn events from a Uniswap V3 pool via Infura (Base mainnet)
- Batches eth_getLogs in 2 000-block chunks with 100 ms inter-batch delay
- Decodes each log with viem and writes one JSON Line per event
- Supports resume: reads last block from existing cache file on re-run
- Retries with exponential back-off on 429 / rate-limit errors
- Prints per-batch progress: "Fetching blocks X-Y... N events (B/T batches)"

Also adds package.json, tsconfig.json, and cache/.gitkeep.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

onchain/script/backtesting/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "backtesting",
+  "version": "0.0.1",
+  "type": "module",
+  "scripts": {
+    "fetch": "tsx fetch-events.ts"
+  },
+  "dependencies": {
+    "viem": "^2.22.13"
+  },
+  "devDependencies": {
+    "@types/node": "^24.0.0",
+    "tsx": "^4.19.0",
+    "typescript": "^5.7.0"
+  }
+}