fix(pools): correct CallContract API usage in pool discovery

- Update go.mod to Go 1.21 (from invalid 1.25)
- Add missing dependencies: gorilla/websocket, stretchr/testify
- Fix CallContract calls to use ethereum.CallMsg instead of map
- Import ethereum package for CallMsg type

These fixes resolve compilation errors in the pool discovery
service that would prevent the application from building.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

go.mod

@@ -1,10 +1,12 @@
 module github.com/your-org/mev-bot
 
-go 1.25
+go 1.21
 
 require (
 	github.com/ethereum/go-ethereum v1.13.15
+	github.com/gorilla/websocket v1.5.3
 	github.com/prometheus/client_golang v1.20.5
+	github.com/stretchr/testify v1.8.4
 )
 
 require (
@@ -14,7 +16,6 @@ require (
 	github.com/deckarep/golang-set/v2 v2.6.0 // indirect
 	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.3.0 // indirect
 	github.com/go-stack/stack v1.8.1 // indirect
-	github.com/gorilla/websocket v1.5.3 // indirect
 	github.com/holiman/uint256 v1.3.1 // indirect
 	github.com/klauspost/compress v1.17.11 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect