Optimize ObjectId.__str__()

Like #2656, I spotted this function taking ~0.9% of request time in a project using mongoengine.

[`bytes.hex()`](https://docs.python.org/3/library/stdtypes.html#bytes.hex) was added in Python 3.5 and does the same as `binascii.hexlify(...).decode()` but faster, so I've replaced it here. (The `binascii.hexlify()` docs also now point to `bytes.hex()` as a faster alternative.)

Benchmarked again using [`richbench`](https://github.com/tonybaloney/rich-bench) with the below script.

<details>

<summary><code>bench_objectid_str.py</code></summary>

```python
from __future__ import annotations

import binascii
import os

class ObjectIdBefore:
    __slots__ = ("__id",)

    def __init__(self) -> None:
        self.__id = os.urandom(12)

    def __str__(self) -> str:
        return binascii.hexlify(self.__id).decode()

class ObjectIdAfter:
    __slots__ = ("__id",)

    def __init__(self) -> None:
        self.__id = os.urandom(12)

    def __str__(self) -> str:
        return self.__id.hex()

test_oids_before = [ObjectIdBefore() for _ in range(100)]
test_oids_after = [ObjectIdAfter() for _ in range(100)]

def bench_str_before():
    for oid in test_oids_before:
        for _ in range(100_000):
            str(oid)

def bench_str_after():
    for oid in test_oids_after:
        for _ in range(100_000):
            str(oid)

__benchmarks__ = [
    (bench_str_before, bench_str_after, "str(ObjectId) - hex conversion"),
]
```

</details>

Results show a ~1.4x speedup:

```
$ uvx -p 3.13 richbench .
                                            Benchmarks, repeat=5, number=5
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━┳━━━━━━━━━┳━━━━━━━━━┳━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━┓
┃                      Benchmark ┃ Min     ┃ Max     ┃ Mean    ┃ Min (+)         ┃ Max (+)         ┃ Mean (+)        ┃
┡━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━╇━━━━━━━━━╇━━━━━━━━━╇━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━┩
│ str(ObjectId) - hex conversion │ 3.000   │ 3.061   │ 3.019   │ 2.169 (1.4x)    │ 2.231 (1.4x)    │ 2.196 (1.4x)    │
└────────────────────────────────┴─────────┴─────────┴─────────┴─────────────────┴─────────────────┴─────────────────┘
```

Author: adamchainz

bson/objectid.py

@@ -15,7 +15,6 @@
 """Tools for working with MongoDB ObjectIds."""
 from __future__ import annotations
 
-import binascii
 import datetime
 import os
 import struct
@@ -234,7 +233,7 @@ def __setstate__(self, value: Any) -> None:
             self.__id = oid
 
     def __str__(self) -> str:
-        return binascii.hexlify(self.__id).decode()
+        return self.__id.hex()
 
     def __repr__(self) -> str:
         return f"ObjectId('{self!s}')"