chore: fix clippy warning in rust 1.87.0

The code is shorter and probably clearer in its intent now.

The error was:
```
warning: use `std::ptr::eq` when comparing raw pointers
   --> rusqlite_migration/src/lib.rs:108:35
    |
108 |             (Some(a), Some(b)) => addr_of!(*a) as usize == addr_of!(*b) as usize,
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::eq(addr_of!(*a), addr_of!(*b))`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_eq
    = note: `#[warn(clippy::ptr_eq)]` on by default

warning: use `std::ptr::eq` when comparing raw pointers
   --> rusqlite_migration/src/lib.rs:114:35
    |
114 |             (Some(a), Some(b)) => addr_of!(*a) as usize == addr_of!(*b) as usize,
    |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `std::ptr::eq(addr_of!(*a), addr_of!(*b))`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_eq

warning: `rusqlite_migration` (lib) generated 2 warnings (run `cargo clippy --fix --lib -p rusqlite_migration` to apply 2 suggestions)
```

Author: cljoly

rusqlite_migration/src/lib.rs

@@ -103,15 +103,17 @@ pub struct M<'u> {
 
 impl PartialEq for M<'_> {
     fn eq(&self, other: &Self) -> bool {
+        use std::ptr;
+
         let equal_up_hooks = match (self.up_hook.as_ref(), other.up_hook.as_ref()) {
             (None, None) => true,
-            (Some(a), Some(b)) => addr_of!(*a) as usize == addr_of!(*b) as usize,
+            (Some(a), Some(b)) => ptr::eq(addr_of!(*a), addr_of!(*b)),
             _ => false,
         };
 
         let equal_down_hooks = match (self.down_hook.as_ref(), other.down_hook.as_ref()) {
             (None, None) => true,
-            (Some(a), Some(b)) => addr_of!(*a) as usize == addr_of!(*b) as usize,
+            (Some(a), Some(b)) => ptr::eq(addr_of!(*a), addr_of!(*b)),
             _ => false,
         };