Speed up ProhibitSurrogateCharactersValidator

I've noticed that this validator is using a per-character loop. Replacing it
with a regex results in a pretty significant speedup. Here are results from
my benchmark:

    String length      Old implementation    New implementation
                           time (sec)            time (sec)

              1          2.833e-07             1.765e-07
             10          5.885e-07             2.030e-07
            100          3.598e-06             4.144e-07
           1000          3.329e-05             2.463e-06
          10000          0.0003338             2.449e-05
         100000          0.003338              0.0002284
        1000000          0.03333               0.002278
       10000000          0.3389                0.02377
      100000000          3.250                 0.2365

For large strings, the speedups are more than an order of magnitude.

Author: SpecLad

rest_framework/validators.py

@@ -6,6 +6,8 @@
 object creation, and makes it possible to switch between using the implicit
 `ModelSerializer` class and an equivalent explicit `Serializer` class.
 """
+import re
+
 from django.core.exceptions import FieldError
 from django.db import DataError
 from django.db.models import Exists
@@ -216,13 +218,14 @@ def __eq__(self, other):
 
 
 class ProhibitSurrogateCharactersValidator:
+    _regex = re.compile(r'[\ud800-\udfff]')
+
     message = _('Surrogate characters are not allowed: U+{code_point:X}.')
     code = 'surrogate_characters_not_allowed'
 
     def __call__(self, value):
-        for surrogate_character in (ch for ch in str(value)
-                                    if 0xD800 <= ord(ch) <= 0xDFFF):
-            message = self.message.format(code_point=ord(surrogate_character))
+        if match := self._regex.search(str(value)):
+            message = self.message.format(code_point=ord(match.group()))
             raise ValidationError(message, code=self.code)
 
     def __eq__(self, other):