fix: resolve clippy warnings (matches!, map_or, redundant guard, unnecessary allocations)

src/api/types.rs

@@ -141,6 +141,7 @@ pub(crate) struct OutputTokensDetails {
 }
 
 #[derive(Serialize, Clone)]
+#[derive(Default)]
 pub(crate) struct Reasoning {
     pub effort: Option<String>,
     pub summary: Option<String>,
@@ -161,8 +162,8 @@ impl Usage {
     /// Estimate token counts from actual text.
     /// Uses ~4 chars/token heuristic (standard GPT tokenizer average).
     pub fn estimate(input_text: &str, output_text: &str) -> Self {
-        let input_tokens = (input_text.len() as u64 + 3) / 4;
-        let output_tokens = (output_text.len() as u64 + 3) / 4;
+        let input_tokens = (input_text.len() as u64).div_ceil(4);
+        let output_tokens = (output_text.len() as u64).div_ceil(4);
         Self {
             input_tokens,
             input_tokens_details: InputTokensDetails { cached_tokens: 0 },
@@ -189,14 +190,6 @@ impl Default for Usage {
     }
 }
 
-impl Default for Reasoning {
-    fn default() -> Self {
-        Self {
-            effort: None,
-            summary: None,
-        }
-    }
-}
 
 impl Default for TextFormat {
     fn default() -> Self {