fix(core): silence three clippy warnings blocking CI gate

* line_index.rs: replace manual `x % BLOCK_SIZE == 0` with
  `.is_multiple_of(BLOCK_SIZE)` (Rust 1.81+).

* line_index.rs: gate three pub(crate) accessor methods
  (`sampled_offsets`, `total_lines`, `has_trailing_newline`) behind
  `#[cfg(test)]`. They are only consumed by tests in file_reader.rs;
  marking them test-only removes them from production builds entirely,
  eliminating the dead_code warning without suppressing it.

* json.rs: drop redundant `Some(... .ok()?)` wrapper in
  parse_json_object_with_duplicates. `.ok()` already returns Option,
  so wrapping it in Some and unwrapping with ? was a no-op.

No behavior change. Unblocks `cargo clippy --workspace -- -D warnings`.

crates/core/src/io/line_index.rs

@@ -158,7 +158,7 @@ impl LineIndex {
 
         // If the junction falls on a block boundary, record the start offset
         // (analogous to from_bytes always pushing offset 0 for line 0).
-        if starts_new_line && (old_total as usize) % BLOCK_SIZE == 0 {
+        if starts_new_line && (old_total as usize).is_multiple_of(BLOCK_SIZE) {
             self.sampled_offsets.push(start_offset);
         }
 
@@ -212,15 +212,17 @@ impl LineIndex {
         self.total_lines as usize
     }
 
-    // ─── getter 方法 ────────────────────────────────────────────────────
+    #[cfg(test)]
     pub(crate) fn sampled_offsets(&self) -> &[u64] {
         &self.sampled_offsets
     }
 
+    #[cfg(test)]
     pub(crate) fn total_lines(&self) -> u64 {
         self.total_lines
     }
 
+    #[cfg(test)]
     pub(crate) fn has_trailing_newline(&self) -> bool {
         self.has_trailing_newline
     }

crates/core/src/parser/json.rs

@@ -22,8 +22,8 @@ use std::collections::{HashMap, HashSet};
 // 默认的 serde_json::from_str::<HashMap<_, _>>() 遇到重复键时会采用"后者覆盖前者"（last-wins），
 // 前面的值被静默丢弃。这里我们通过自定义 Visitor 在反序列化过程中逐个观察 key-value 对，
 // 在保持 last-wins 行为的同时，将重复 key 的所有值记录到 DuplicateKey 中。
-use serde::de::{MapAccess, Visitor};
 use serde::Deserializer;
+use serde::de::{MapAccess, Visitor};
 
 // serde_json::Value — 来自 serde_json 库（Rust 中最流行的 JSON 处理库）。
 // Value 是一个枚举类型，可以表示任意 JSON 值：
@@ -83,7 +83,10 @@ pub fn detect_json_log(line: &str) -> bool {
     //    则匹配成功。_ 是通配符，表示"不关心对象里面的具体内容"。
     //
     // 如果匹配到 Ok(Value::Object(_)) 返回 true，否则返回 false。
-    matches!(serde_json::from_str::<Value>(strip_bom(line)), Ok(Value::Object(_)))
+    matches!(
+        serde_json::from_str::<Value>(strip_bom(line)),
+        Ok(Value::Object(_))
+    )
 }
 
 // ─── DuplicateKeyVisitor ──────────────────────────────────────────────────
@@ -147,7 +150,7 @@ fn parse_json_object_with_duplicates(
     json: &str,
 ) -> Option<(serde_json::Map<String, Value>, Vec<DuplicateKey>)> {
     let mut deserializer = serde_json::Deserializer::from_str(json);
-    Some(deserializer.deserialize_map(DuplicateKeyVisitor).ok()?)
+    deserializer.deserialize_map(DuplicateKeyVisitor).ok()
 }
 
 // ─── take_string_field_from_map 辅助函数 ──────────────────────────────────
@@ -189,7 +192,8 @@ pub fn parse_line(line: &str) -> Option<LogEntry> {
     let (mut obj, duplicate_keys) = parse_json_object_with_duplicates(line)?;
 
     let raw_line = line.to_string();
-    let timestamp = take_string_field_from_map(&mut obj, &["timestamp", "time", "ts", "@timestamp"]);
+    let timestamp =
+        take_string_field_from_map(&mut obj, &["timestamp", "time", "ts", "@timestamp"]);
     let level = take_string_field_from_map(&mut obj, &["level", "lvl", "severity"])
         .map(|s| s.parse::<LogLevel>().unwrap_or_else(|e| match e {}));
 
@@ -513,8 +517,14 @@ mod tests {
         assert_eq!(entry.duplicate_keys.len(), 1);
         assert_eq!(entry.duplicate_keys[0].key, "message");
         assert_eq!(entry.duplicate_keys[0].values.len(), 2);
-        assert_eq!(entry.duplicate_keys[0].values[0], Value::String("first".into()));
-        assert_eq!(entry.duplicate_keys[0].values[1], Value::String("second".into()));
+        assert_eq!(
+            entry.duplicate_keys[0].values[0],
+            Value::String("first".into())
+        );
+        assert_eq!(
+            entry.duplicate_keys[0].values[1],
+            Value::String("second".into())
+        );
     }
 
     #[test]