[3.10] bpo-45461: Fix IncrementalDecoder and StreamReader in the "unicode-escape" codec (GH-28939) (GH-28943)

They support now splitting escape sequences between input chunks.

Add the third parameter "final" in codecs.unicode_escape_decode().
It is True by default to match the former behavior.
(cherry picked from commit c96d1546b11b4c282a7e21737cb1f5d16349656d)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index 328a47b..153912b 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -114,7 +114,7 @@ def check_partial(self, input, partialresults):
         q = Queue(b"")
         r = codecs.getreader(self.encoding)(q)
         result = ""
-        for (c, partialresult) in zip(input.encode(self.encoding), partialresults):
+        for (c, partialresult) in zip(input.encode(self.encoding), partialresults, strict=True):
             q.write(bytes([c]))
             result += r.read()
             self.assertEqual(result, partialresult)
@@ -125,7 +125,7 @@ def check_partial(self, input, partialresults):
         # do the check again, this time using an incremental decoder
         d = codecs.getincrementaldecoder(self.encoding)()
         result = ""
-        for (c, partialresult) in zip(input.encode(self.encoding), partialresults):
+        for (c, partialresult) in zip(input.encode(self.encoding), partialresults, strict=True):
             result += d.decode(bytes([c]))
             self.assertEqual(result, partialresult)
         # check that there's nothing left in the buffers
@@ -135,7 +135,7 @@ def check_partial(self, input, partialresults):
         # Check whether the reset method works properly
         d.reset()
         result = ""
-        for (c, partialresult) in zip(input.encode(self.encoding), partialresults):
+        for (c, partialresult) in zip(input.encode(self.encoding), partialresults, strict=True):
             result += d.decode(bytes([c]))
             self.assertEqual(result, partialresult)
         # check that there's nothing left in the buffers
@@ -2341,7 +2341,11 @@ def test_unicode_escape(self):
                          (r"\x5c\x55\x30\x30\x31\x31\x30\x30\x30\x30", 10))
 
 
-class UnicodeEscapeTest(unittest.TestCase):
+class UnicodeEscapeTest(ReadTest, unittest.TestCase):
+    encoding = "unicode-escape"
+
+    test_lone_surrogates = None
+
     def test_empty(self):
         self.assertEqual(codecs.unicode_escape_encode(""), (b"", 0))
         self.assertEqual(codecs.unicode_escape_decode(b""), ("", 0))
@@ -2428,6 +2432,44 @@ def test_decode_errors(self):
         self.assertEqual(decode(br"\U00110000", "ignore"), ("", 10))
         self.assertEqual(decode(br"\U00110000", "replace"), ("\ufffd", 10))
 
+    def test_partial(self):
+        self.check_partial(
+            "\x00\t\n\r\\\xff\uffff\U00010000",
+            [
+                '',
+                '',
+                '',
+                '\x00',
+                '\x00',
+                '\x00\t',
+                '\x00\t',
+                '\x00\t\n',
+                '\x00\t\n',
+                '\x00\t\n\r',
+                '\x00\t\n\r',
+                '\x00\t\n\r\\',
+                '\x00\t\n\r\\',
+                '\x00\t\n\r\\',
+                '\x00\t\n\r\\',
+                '\x00\t\n\r\\\xff',
+                '\x00\t\n\r\\\xff',
+                '\x00\t\n\r\\\xff',
+                '\x00\t\n\r\\\xff',
+                '\x00\t\n\r\\\xff',
+                '\x00\t\n\r\\\xff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff',
+                '\x00\t\n\r\\\xff\uffff\U00010000',
+            ]
+        )
 
 class RawUnicodeEscapeTest(unittest.TestCase):
     def test_empty(self):