Update script and add README

Author: r-near

contracts/near/eth2-client/src/data/README.md

@@ -0,0 +1,52 @@
+# Test Data Generator
+
+Generates test data for ETH light client integration tests on NEAR.
+
+## Usage
+
+### Generate Sepolia Test Data
+```bash
+cd contracts/near/eth2-client/src/data/
+uv run dump_sepolia_data.py
+```
+
+### Dependencies
+Uses `uv` for fast dependency management:
+```bash
+# Install uv if needed
+curl -LsSf https://astral.sh/uv/install.sh | sh
+
+# Dependencies auto-installed on first run with uv
+# Or manually: uv add requests web3 tqdm eth2spec
+```
+
+### Environment Variables
+- `NETWORK`: Network name (default: `sepolia`)
+- `EXECUTION_RPC`: Ethereum RPC endpoint
+- `CONSENSUS_API`: Beacon chain API endpoint
+- `BLOCK_WINDOW`: Block window size (default: `50`)
+- `BATCH_SIZE`: RPC batch size (default: `50`)
+
+### Output Files
+- `{network}/execution_blocks_{start}_{end}.json`: Execution block headers
+- `{network}/light_client_update_period_{period}.json`: Light client updates
+- `{network}/beacon_header_{slot}.json`: Beacon block headers
+
+## Integration Tests
+
+The script generates data used by:
+- `get_sepolia_test_data()` in `tests/utils.rs`
+- Integration tests in `tests/integration_tests.rs`
+
+### Update Test Data
+1. Run the script to generate new data files
+2. Update hardcoded block numbers and periods in `tests/utils.rs:106-122`
+3. Run tests: `cargo test`
+
+### How It Works
+- Fetches 4 most recent light client update periods
+- Downloads corresponding execution blocks in 2 batches
+- Generates Merkle proofs for block hash verification
+- Creates normalized JSON files matching Rust struct format
+
+The test expects specific file patterns matching the periods and block ranges defined in `utils.rs`.

contracts/near/eth2-client/src/data/dump_sepolia_data.py

@@ -337,8 +337,8 @@ def get_block_number_for_period(period: int) -> int:
 
 
 def main():
-    periods = [925, 926, 927, 928]
-    dump_light_client_updates(periods)
+    # Fetch the 4 most recent light client updates
+    periods = get_recent_light_client_updates(4)
     print(f"🎉 Updates fetched for periods: {periods}")
 
     rev = list(reversed(periods))