feat(agent): add container runtime support and enhance agent configuration

- Introduced ContainerRuntime field in AgentConfig and AgentEnvConfig.
- Added IterAgents and NumAgents functions for agent pool management.
- Updated agent creation and verification endpoints to handle container runtime.
- Enhanced Docker Compose template to support different container runtimes.
- Added runtime endpoint to retrieve agent runtime information.

agent/pkg/agent/agent_pool.go

@@ -1,6 +1,7 @@
 package agent
 
 import (
+	"iter"
 
 	"github.com/puzpuzpuz/xsync/v4"
 	"github.com/yusing/go-proxy/internal/common"
@@ -52,6 +53,14 @@ func ListAgents() []*AgentConfig {
 	return agents
 }
 
+func IterAgents() iter.Seq2[string, *AgentConfig] {
+	return agentPool.Range
+}
+
+func NumAgents() int {
+	return agentPool.Size()
+}
+
 func getAgentByAddr(addr string) (agent *AgentConfig, ok bool) {
 	agent, ok = agentPool.Load(addr)
 	return