perf(python): Directly access the key-value pairs of a dict (#1970)

## What does this PR do?

In Python, to implement a linear memory structure that stores key-value
pairs, we can traverse them in the order of insertion like accessing an
array. However, Cython does not provide a direct access interface, and
these interfaces are internal in CPython, requiring compatibility work
to use them correctly. Nevertheless, we can still use the`PyDict_Next`
interface to replace the `items` method. Essentially, `items` use
`PyDict_Next` to append to a list. Doing so can reduce the copying
overhead.

## Related issues

## Does this PR introduce any user-facing change?

- [ ] Does this PR introduce any public API change?
- [ ] Does this PR introduce any binary protocol compatibility change?

## Benchmark
For large dict
```
[dict_item] 541 us +- 39 us -> [dict_next]  535 us +- 35 us: 1.00x faster

[dict_item] 119.8 MiB +- 1344.0 KiB -> [dict_next] 118.8 MiB +- 1338.4 KiB: 1.01x faster
```

python/pyfury/_serialization.pyx

@@ -44,6 +44,7 @@ from pyfury.util import is_little_endian
 from libc.stdint cimport *
 from libcpp.vector cimport vector
 from cpython cimport PyObject
+from cpython.dict cimport PyDict_Next
 from cpython.ref cimport *
 from cpython.list cimport PyList_New, PyList_SET_ITEM
 from cpython.tuple cimport PyTuple_New, PyTuple_SET_ITEM
@@ -2049,7 +2050,13 @@ cdef class MapSerializer(Serializer):
         buffer.write_varint32(len(value))
         cdef ClassInfo key_classinfo
         cdef ClassInfo value_classinfo
-        for k, v in value.items():
+        cdef int64_t key_addr, value_addr
+        cdef Py_ssize_t pos = 0
+        while PyDict_Next(value, &pos, <PyObject **>&key_addr, <PyObject **>&value_addr) != 0:
+            k = int2obj(key_addr)
+            Py_INCREF(k)
+            v = int2obj(value_addr)
+            Py_INCREF(v)
             key_cls = type(k)
             if key_cls is str:
                 buffer.write_int16(NOT_NULL_STRING_FLAG)
@@ -2122,7 +2129,13 @@ cdef class MapSerializer(Serializer):
     cpdef inline xwrite(self, Buffer buffer, o):
         cdef dict value = o
         buffer.write_varint32(len(value))
-        for k, v in value.items():
+        cdef int64_t key_addr, value_addr
+        cdef Py_ssize_t pos = 0
+        while PyDict_Next(value, &pos, <PyObject **>&key_addr, <PyObject **>&value_addr) != 0:
+            k = int2obj(key_addr)
+            Py_INCREF(k)
+            v = int2obj(value_addr)
+            Py_INCREF(v)
             self.fury.xserialize_ref(
                 buffer, k, serializer=self.key_serializer
             )