Fix local chain methods over WebSocket

[GhostStar]

Summary

• handle eth_chainId and net_version before the WebSocket unsubscribe path
• preserve subscription cancellation behavior for local unsubscribe methods
• cover both HTTP and WebSocket request contexts in the local processor test

Root cause

Every request received through the WebSocket server has a non-nil subscription context. The local request processor treated every local method with such a context as an unsubscribe request and attempted to read params[0]. Standard parameterless methods such as eth_chainId and net_version therefore failed with value not exists.

Tests

• go test ./internal/upstreams/flow -run TestLocalRequestProcessor -count=1
• go test ./internal/upstreams/flow -count=1
• go test ./... -count=1
• make build