fix: resolve clippy warnings

Reduce clippy warnings from54 to16 by fixing mechanical issues:

- collapsible_if: collapse nested if-let chains with let-chains
- clone_on_copy: remove unnecessary .clone() on Copy types
- manual_clamp: replace .max().min() with .clamp()
- unnecessary_cast: remove redundant type casts
- collapsible_else_if: flatten else-if chains
- contains_vs_iter_any: replace .iter().any() with .contains()
- unnecessary_closure: replace .or_else(|| x) with .or(x)
- useless_conversion: remove redundant .into() calls
- is_none_or: replace .map_or(true, ...) with .is_none_or(...)
- while_let_loop: convert loop with if-let-break to while-let

Remaining16 warnings are design-level issues (too_many_arguments,
await_holding_lock, type_complexity, new_ret_no_self) that require
architectural changes to fix.

src/protocol/constants.rs

@@ -160,7 +160,7 @@ pub const MAX_TLS_CHUNK_SIZE: usize = 16384 + 256;
 
 /// Secure Intermediate payload is expected to be 4-byte aligned.
 pub fn is_valid_secure_payload_len(data_len: usize) -> bool {
-    data_len % 4 == 0
+    data_len.is_multiple_of(4)
 }
 
 /// Compute Secure Intermediate payload length from wire length.
@@ -179,7 +179,7 @@ pub fn secure_padding_len(data_len: usize, rng: &SecureRandom) -> usize {
         is_valid_secure_payload_len(data_len),
         "Secure payload must be 4-byte aligned, got {data_len}"
     );
-    (rng.range(3) + 1) as usize
+    rng.range(3) + 1
 }
 
 // ============= Timeouts =============
@@ -231,7 +231,6 @@ pub static RESERVED_NONCE_CONTINUES: &[[u8; 4]] = &[
 // ============= RPC Constants (for Middle Proxy) =============
 
 /// RPC Proxy Request
-
 /// RPC Flags (from Erlang mtp_rpc.erl)
 pub const RPC_FLAG_NOT_ENCRYPTED: u32 = 0x2;
 pub const RPC_FLAG_HAS_AD_TAG: u32    = 0x8;

src/protocol/frame.rs

@@ -85,7 +85,7 @@ impl FrameMode {
 pub fn validate_message_length(len: usize) -> bool {
     use super::constants::{MIN_MSG_LEN, MAX_MSG_LEN, PADDING_FILLER};
     
-    len >= MIN_MSG_LEN && len <= MAX_MSG_LEN && len % PADDING_FILLER.len() == 0
+    (MIN_MSG_LEN..=MAX_MSG_LEN).contains(&len) && len.is_multiple_of(PADDING_FILLER.len())
 }
 
 #[cfg(test)]

src/protocol/tls.rs

@@ -335,7 +335,7 @@ pub fn validate_tls_handshake(
             // This is a quirk in some clients that use uptime instead of real time
             let is_boot_time = timestamp < 60 * 60 * 24 * 1000; // < ~2.7 years in seconds
             
-            if !is_boot_time && (time_diff < TIME_SKEW_MIN || time_diff > TIME_SKEW_MAX) {
+            if !is_boot_time && !(TIME_SKEW_MIN..=TIME_SKEW_MAX).contains(&time_diff) {
                 continue;
             }
         }
@@ -393,7 +393,7 @@ pub fn build_server_hello(
 ) -> Vec<u8> {
     const MIN_APP_DATA: usize = 64;
     const MAX_APP_DATA: usize = 16640; // RFC 8446 §5.2 upper bound
-    let fake_cert_len = fake_cert_len.max(MIN_APP_DATA).min(MAX_APP_DATA);
+    let fake_cert_len = fake_cert_len.clamp(MIN_APP_DATA, MAX_APP_DATA);
     let x25519_key = gen_fake_x25519_key(rng);
     
     // Build ServerHello
@@ -525,10 +525,10 @@ pub fn extract_sni_from_client_hello(handshake: &[u8]) -> Option<String> {
                 if sn_pos + name_len > sn_end {
                     break;
                 }
-                if name_type == 0 && name_len > 0 {
-                    if let Ok(host) = std::str::from_utf8(&handshake[sn_pos..sn_pos + name_len]) {
-                        return Some(host.to_string());
-                    }
+                if name_type == 0 && name_len > 0
+                    && let Ok(host) = std::str::from_utf8(&handshake[sn_pos..sn_pos + name_len])
+                {
+                    return Some(host.to_string());
                 }
                 sn_pos += name_len;
             }
@@ -571,7 +571,7 @@ pub fn extract_alpn_from_client_hello(handshake: &[u8]) -> Vec<Vec<u8>> {
             let list_len = u16::from_be_bytes([handshake[pos], handshake[pos+1]]) as usize;
             let mut lp = pos + 2;
             let list_end = (pos + 2).saturating_add(list_len).min(pos + elen);
-            while lp + 1 <= list_end {
+            while lp < list_end {
                 let plen = handshake[lp] as usize;
                 lp += 1;
                 if lp + plen > list_end { break; }