gh-75876: Correct the memory use declared by some bigmem tests

Measured with a limited address space and the peak RSS of the process:

* TupleTest.test_repeat_large_2 keeps 3 tuples of pointers alive, as its
  siblings do, but declared the count for a 32-bit build.
* The md5 tests hash the data and a io.BytesIO() copy of it.
* testDecompress4G keeps the data, the compressed and the decompressed
  bytes alive, and the decompressor grows its output buffer.
* test_huge_string_builtins uses 3 times the string size, not 2.
* test_large_subn uses a bit more than the 18 times it declared.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_bigmem.py

@@ -901,7 +901,7 @@ def test_repeat_small(self, size):
     def test_repeat_large(self, size):
         return self.basic_test_repeat(size)
 
-    @bigmemtest(size=_1G - 1, memuse=12)
+    @bigmemtest(size=_1G - 1, memuse=pointer_size * 3)
     def test_repeat_large_2(self, size):
         return self.basic_test_repeat(size)
 

Lib/test/test_hashlib.py

@@ -691,12 +691,12 @@ def test_case_md5_2(self):
         )
 
     @unittest.skipIf(sys.maxsize < _4G + 5, 'test cannot run on 32-bit systems')
-    @bigmemtest(size=_4G + 5, memuse=1, dry_run=False)
+    @bigmemtest(size=_4G + 5, memuse=2, dry_run=False)
     def test_case_md5_huge(self, size):
         self.check('md5', b'A'*size, 'c9af2dff37468ce5dfee8f2cfc0a9c6d')
 
     @unittest.skipIf(sys.maxsize < _4G - 1, 'test cannot run on 32-bit systems')
-    @bigmemtest(size=_4G - 1, memuse=1, dry_run=False)
+    @bigmemtest(size=_4G - 1, memuse=2, dry_run=False)
     def test_case_md5_uintmax(self, size):
         self.check('md5', b'A'*size, '28138d306ff1b8281f1a9067e1a1a2b3')
 

Lib/test/test_re.py

@@ -2251,7 +2251,7 @@ def test_large_search(self, size):
 
     # The huge memuse is because of re.sub() using a list and a join()
     # to create the replacement result.
-    @bigmemtest(size=_2G, memuse=16 + 2)
+    @bigmemtest(size=_2G, memuse=16 + 3)
     def test_large_subn(self, size):
         # Issue #10182: indices were 32-bit-truncated.
         s = 'a' * size

Lib/test/test_tcl.py

@@ -805,7 +805,7 @@ def test_huge_string_call(self, size):
 
     @support.cpython_only
     @unittest.skipUnless(INT_MAX < PY_SSIZE_T_MAX, "needs UINT_MAX < SIZE_MAX")
-    @support.bigmemtest(size=INT_MAX + 1, memuse=2, dry_run=False)
+    @support.bigmemtest(size=INT_MAX + 1, memuse=3, dry_run=False)
     def test_huge_string_builtins(self, size):
         tk = self.interp.tk
         value = '1' + ' ' * size

Lib/test/test_zlib.py

@@ -1090,7 +1090,7 @@ def testEOFError(self):
         self.assertRaises(EOFError, zlibd.decompress, b"")
 
     @support.skip_if_pgo_task
-    @bigmemtest(size=_4G + 100, memuse=3.3)
+    @bigmemtest(size=_4G + 100, memuse=4.5)
     def testDecompress4G(self, size):
         # "Test zlib._ZlibDecompressor.decompress() with >4GiB input"
         blocksize = min(10 * 1024 * 1024, size)