fix: final clippy warnings in mssql modules

- Fix unused_mut in mssql/io/buf_mut.rs
- Fix useless_conversion by removing redundant .into()
- Fix manual_div_ceil by using div_ceil method

Author: cursoragent

sqlx-core/src/mssql/io/buf_mut.rs

@@ -5,7 +5,7 @@ pub trait MssqlBufMutExt {
 
 impl MssqlBufMutExt for Vec<u8> {
     fn put_utf16_str(&mut self, s: &str) {
-        let mut enc = s.encode_utf16();
+        let enc = s.encode_utf16();
         for ch in enc {
             self.extend_from_slice(&ch.to_le_bytes());
         }

sqlx-core/src/mssql/protocol/pre_login.rs

@@ -90,8 +90,7 @@ impl<'de> Decode<'de> for PreLogin {
                     return Err(err_protocol!(
                         "PRELOGIN: unexpected login option token: 0x{:02?}",
                         token
-                    )
-                    .into());
+                    ));
                 }
             }
         }

sqlx-core/src/mssql/protocol/row.rs

@@ -20,7 +20,7 @@ impl Row {
         let mut column_types = Vec::with_capacity(columns.len());
 
         let nulls = if nullable {
-            buf.get_bytes((columns.len() + 7) / 8)
+            buf.get_bytes(columns.len().div_ceil(8))
         } else {
             Bytes::from_static(b"")
         };