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/error.rs

@@ -91,7 +91,7 @@ impl From<StreamError> for std::io::Error {
                 std::io::Error::new(std::io::ErrorKind::UnexpectedEof, err)
             }
             StreamError::Poisoned { .. } => {
-                std::io::Error::new(std::io::ErrorKind::Other, err)
+                std::io::Error::other(err)
             }
             StreamError::BufferOverflow { .. } => {
                 std::io::Error::new(std::io::ErrorKind::OutOfMemory, err)
@@ -100,7 +100,7 @@ impl From<StreamError> for std::io::Error {
                 std::io::Error::new(std::io::ErrorKind::InvalidData, err)
             }
             StreamError::PartialRead { .. } | StreamError::PartialWrite { .. } => {
-                std::io::Error::new(std::io::ErrorKind::Other, err)
+                std::io::Error::other(err)
             }
         }
     }
@@ -135,12 +135,7 @@ impl Recoverable for StreamError {
     }
     
     fn can_continue(&self) -> bool {
-        match self {
-            Self::Poisoned { .. } => false,
-            Self::UnexpectedEof => false,
-            Self::BufferOverflow { .. } => false,
-            _ => true,
-        }
+        !matches!(self, Self::Poisoned { .. } | Self::UnexpectedEof | Self::BufferOverflow { .. })
     }
 }