relay(BSC): adaptive source logs, START_BLOCK parsing, docs, env example

- RelayService: chunked eth_getLogs + adaptive split for strict RPCs
- config: explicit START_BLOCK=latest vs numeric
- README: topology, START_BLOCK, fund script, cast examples
- .env.bsc.example: committed template (secrets stay in .env.bsc)

Made-with: Cursor

services/relay/.env.bsc.example

@@ -0,0 +1,25 @@
+# Copy to .env.bsc and adjust. start-relay.sh loads parent smom-dbis-138/.env for PRIVATE_KEY.
+# RPC_URL_138: use Core RPC on LAN for deploy; public RPC ok for read-only relay scans.
+RPC_URL_138=http://192.168.11.211:8545
+CCIP_ROUTER_CHAIN138=0x42DAb7b888Dd382bD5Adcf9E038dBF1fD03b4817
+CCIPWETH9_BRIDGE_CHAIN138=0xcacfd227A040002e49e2e01626363071324f820a
+SOURCE_CHAIN_SELECTOR=138
+
+DEST_CHAIN_NAME=BSC
+DEST_CHAIN_ID=56
+DEST_RPC_URL=https://bsc.publicnode.com
+DEST_CHAIN_SELECTOR=11344663589394136015
+DEST_RELAY_ROUTER=0x4d9Bc6c74ba65E37c4139F0aEC9fc5Ddff28Dcc4
+DEST_RELAY_BRIDGE=0x886C6A4ABC064dbf74E7caEc460b7eeC31F1b78C
+DEST_WETH9_ADDRESS=0xe0E93247376aa097dB308B92e6Ba36bA015535D0
+
+RELAYER_PRIVATE_KEY=${PRIVATE_KEY}
+RELAYER_ADDRESS=0x4A666F96fC8764181194447A7dFdb7d471b301C8
+
+START_BLOCK=latest
+POLL_INTERVAL=5000
+CONFIRMATION_BLOCKS=1
+MAX_RETRIES=3
+RETRY_DELAY=5000
+LOG_LEVEL=info
+DEST_RELAY_BRIDGE_ALLOWLIST=0x886C6A4ABC064dbf74E7caEc460b7eeC31F1b78C