lua: 吸收 llmsproxy 适配器高级特性（worker 池/静态预提取/动态签名钩子）

- 适配器 worker 池化：单 LState+全局锁（串行瓶颈）→ 每 adapter 一个 gopher-lua
  LState 池，按使用该 adapter 的源并发上限求和配置池大小，并发 transform 互不阻塞
- staticInfo 预提取：name/version/endpoint/headers 加载期编译缓存，Endpoint/Headers
  读缓存不占 worker；加载即预编译首个 worker
- build_headers 动态钩子 + hmac/sha256/base64/tohex 全局：签名型上游（kimicode 等）可接入
- provider applyAdapterHeaders 接入动态头（url/method/body/api_key/timestamp/source 元数据），
  未定义时回落静态 headers，缺省补 Authorization
- LLMSource.MaxConcurrent + core.llm.sources.<name>.max_concurrent，注册时汇总
  VM.ConfigureConcurrency
- 新增 Lua VM 测试（load/transform/build_headers/并发）

验证: go test ./... 27 包 0 失败；Windows 交叉编译通过；部署后 9 adapter 全部预加载

internal/config/registry.go

@@ -185,6 +185,7 @@ var sourceFieldDefs = []struct {
 	{"thinking_enabled", "bool", "深度思考"},
 	{"adapter", "string", "适配器"},
 	{"adapter_path", "string", "适配器路径"},
+	{"max_concurrent", "int", "并发上限"},
 }
 
 // registerSourceDefs 注册 core.llm.sources.<name>.* 的 ConfigDef
@@ -814,6 +815,7 @@ func (r *ConfigRegistry) ToConfig() *types.Config {
 			Adapter:         read(p+".adapter", ""),
 			AdapterPath:     read(p+".adapter_path", ""),
 			ContextWindow:   readInt(p+".context_window", 0),
+			MaxConcurrent:   readInt(p+".max_concurrent", 8),
 			ThinkingEnabled: readBool(p+".thinking_enabled", false),
 		})
 	}