Zero clippy warnings: fix all 32 remaining

- Iterator::find() replaces manual loops (6 sites)
- Index-only loops → iterators (4 sites)
- Identical if-blocks merged
- Box large MkvStream WriteState enum variant
- Vec macro initializers, late init fixes
- Unused fields prefixed with underscore (format spec fields)
- Dead code removed or documented

0 clippy warnings. 319 tests passing.

src/mux/codec/ac3.rs

@@ -101,12 +101,7 @@ impl CodecParser for Ac3Parser {
 
 /// Find AC3/E-AC-3 syncword (0x0B77) in data.
 fn find_ac3_sync(data: &[u8]) -> Option<usize> {
-    for i in 0..data.len().saturating_sub(1) {
-        if data[i] == 0x0B && data[i + 1] == 0x77 {
-            return Some(i);
-        }
-    }
-    None
+    (0..data.len().saturating_sub(1)).find(|&i| data[i] == 0x0B && data[i + 1] == 0x77)
 }
 
 /// Extract bsid from an AC-3/E-AC-3 frame starting at the syncword.

src/mux/codec/dts.rs

@@ -70,16 +70,12 @@ pub fn find_dts_hd_ext_sync(data: &[u8]) -> Option<usize> {
     if data.len() < 4 {
         return None;
     }
-    for i in 0..=data.len() - 4 {
-        if data[i] == DTS_HD_EXT_SYNC[0]
+    (0..=data.len() - 4).find(|&i| {
+        data[i] == DTS_HD_EXT_SYNC[0]
             && data[i + 1] == DTS_HD_EXT_SYNC[1]
             && data[i + 2] == DTS_HD_EXT_SYNC[2]
             && data[i + 3] == DTS_HD_EXT_SYNC[3]
-        {
-            return Some(i);
-        }
-    }
-    None
+    })
 }
 
 /// Calculate DTS-HD extension frame size from the extension header.

src/mux/codec/h264.rs

@@ -110,15 +110,16 @@ impl CodecParser for H264Parser {
         // pictureParameterSetLength = pps.len()
         // pictureParameterSetNALUnit = pps
 
-        let mut record = Vec::new();
-        record.push(1); // configurationVersion
-        record.push(sps[1]); // profile
-        record.push(sps[2]); // compatibility
-        record.push(sps[3]); // level
-        record.push(0xFF); // 6 bits reserved (111111) + 2 bits lengthSizeMinusOne (11 = 3)
-        record.push(0xE1); // 3 bits reserved (111) + 5 bits numSPS (1)
-        record.push((sps.len() >> 8) as u8);
-        record.push(sps.len() as u8);
+        let mut record = vec![
+            1,        // configurationVersion
+            sps[1],   // profile
+            sps[2],   // compatibility
+            sps[3],   // level
+            0xFF,     // 6 bits reserved (111111) + 2 bits lengthSizeMinusOne (11 = 3)
+            0xE1,     // 3 bits reserved (111) + 5 bits numSPS (1)
+            (sps.len() >> 8) as u8,
+            sps.len() as u8,
+        ];
         record.extend_from_slice(sps);
         record.push(1); // numPPS
         record.push((pps.len() >> 8) as u8);
@@ -179,12 +180,7 @@ pub fn find_start_code(data: &[u8], from: usize) -> Option<usize> {
     if data.len() < from + 3 {
         return None;
     }
-    for i in from..data.len() - 2 {
-        if data[i] == 0x00 && data[i + 1] == 0x00 && data[i + 2] == 0x01 {
-            return Some(i);
-        }
-    }
-    None
+    (from..data.len() - 2).find(|&i| data[i] == 0x00 && data[i + 1] == 0x00 && data[i + 2] == 0x01)
 }
 
 /// Skip past the start code at position `pos`, returning the first byte after it.

src/mux/codec/lpcm.rs

@@ -70,7 +70,7 @@ mod tests {
     fn header_skip_extracts_pcm_data() {
         let mut parser = LpcmParser::new();
         // 4-byte LPCM header + 6 bytes of PCM data
-        let header = vec![0x00, 0x01, 0x00, 0b10_01_0001]; // frame#=1, quant=24bit, rate=48k, ch=1
+        let header = vec![0x00, 0x01, 0x00, 0b1001_0001]; // frame#=1, quant=24bit, rate=48k, ch=1
         let pcm_data = vec![0xDE, 0xAD, 0xBE, 0xEF, 0xCA, 0xFE];
         let mut pes_data = header;
         pes_data.extend_from_slice(&pcm_data);

src/mux/codec/mpeg2.rs

@@ -195,12 +195,7 @@ fn find_start_code(data: &[u8], from: usize) -> Option<usize> {
     if data.len() < from + 3 {
         return None;
     }
-    for i in from..data.len() - 2 {
-        if data[i] == 0x00 && data[i + 1] == 0x00 && data[i + 2] == 0x01 {
-            return Some(i);
-        }
-    }
-    None
+    (from..data.len() - 2).find(|&i| data[i] == 0x00 && data[i + 1] == 0x00 && data[i + 2] == 0x01)
 }
 
 #[cfg(test)]

src/mux/codec/vc1.rs

@@ -122,12 +122,7 @@ impl CodecParser for Vc1Parser {
 }
 
 fn find_next_sc(data: &[u8], from: usize) -> Option<usize> {
-    for i in from..data.len().saturating_sub(2) {
-        if data[i] == 0x00 && data[i + 1] == 0x00 && data[i + 2] == 0x01 {
-            return Some(i);
-        }
-    }
-    None
+    (from..data.len().saturating_sub(2)).find(|&i| data[i] == 0x00 && data[i + 1] == 0x00 && data[i + 2] == 0x01)
 }
 
 #[cfg(test)]