refactor(core): 扫清 v0.1 Phase A 技术债

- 修复测试编译回归：补全 session.rs/cycle.rs 测试模块导入；
convert.rs 2 处 irrefutable if let 改为 let
- composer.rs 迁移至 IR：OpenaiChatMessage → Message，
ContentField/OpenaiContentPart → ContentBlock；删除 set_message_name
和 build_request；developer 消息映射为 Message::System
- knowledge.rs 锁修复：std::sync::Mutex → tokio::sync::Mutex；
search() 优化锁粒度（锁内仅 clone IDs，避免锁内异步 IO）
- 标记 ChatResponse / ToolDefinition 为废弃（#[deprecated(since = "0.1.0")]），
内部使用点加 #[allow(deprecated)] 抑制警告
- clippy 清零：合并冗余 if、手动 strip_prefix 改 strip_prefix、
多处 dead_code 抑制、测试代码清理

src/llm/provider/anthropic.rs

@@ -36,6 +36,7 @@ const DEFAULT_MAX_TOKENS: u32 = 4096;
 pub struct AnthropicProvider {
     http_client: Client,
     base_url: String,
+    #[allow(dead_code)]
     api_key: String,
     model: String,
 }
@@ -586,6 +587,7 @@ enum AnthropicDelta {
 struct AnthropicMessageDeltaInner {
     stop_reason: Option<String>,
     #[serde(default)]
+    #[allow(dead_code)]
     stop_sequence: Option<String>,
 }
 
@@ -599,6 +601,7 @@ pub struct AnthropicSseStream {
     chunks: Pin<Box<dyn Stream<Item = Result<Bytes, LlmError>> + Send>>,
     buffer: String,
     partial: PartialMessageResponse,
+    #[allow(dead_code)]
     next_block_index: u32,
     saw_terminal: bool,
 }

src/llm/provider/openai.rs

@@ -720,8 +720,8 @@ impl Stream for ChunkToEventStream {
                 }
                 let data = if let Some(p) = trimmed.strip_prefix("data: ") {
                     p
-                } else if trimmed.starts_with("data:") {
-                    &trimmed[5..]
+                } else if let Some(p) = trimmed.strip_prefix("data:") {
+                    p
                 } else {
                     continue;
                 };