Update ASan information regarding --without-pymalloc flag (GH-1609)

* Update ASan information regarding --without-pymalloc flag

As discussed with @encukou on the CPython Core sprint on EuroPython 2025.

We initially thought that the `--without-pymalloc` flag is needed due to the fact pymalloc must hit the begining of page when determining if the memory to be freed comes from pymalloc or was allocated by the system malloc. In other words, we thought, that ASan would crash CPython during free of big objects (allocated by system malloc). It may be that this was the case in the past, but it is not the case anymore as the `address_in_range` function used by pymalloc is annotated to be skipped from the ASan instrumentation.

This code can be seen here:
https://github.com/python/cpython/blob/acefb978dcb5dd554e3c49a3015ee5c2ad6bfda1/Objects/obmalloc.c#L2096-L2110

While the annotation macro is defined here:
https://github.com/python/cpython/blob/acefb978dcb5dd554e3c49a3015ee5c2ad6bfda1/Include/pyport.h#L582-L598

And the corresponding attribute is documented in:
* for gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fsanitize_005faddress-function-attribute
* for clang: https://clang.llvm.org/docs/AttributeReference.html#no-sanitize-address-no-address-safety-analysis

* Apply suggestions from code review

* Apply suggestions from code review

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Co-authored-by: Petr Viktorin <[email protected]>

Author: disconnect3d

development-tools/clang.rst

@@ -103,6 +103,10 @@ Then, run ``./configure`` with the relevant flags:
 * ASan: ``--with-address-sanitizer --without-pymalloc``
 * UBsan: ``--with-undefined-behavior-sanitizer``
 
+The ``--without-pymalloc`` option is not necessary (tests should pass without it),
+but disabling pymalloc helps ASan uncover more bugs (ASan does not track
+individual allocations done by pymalloc).
+
 It is OK to specify both sanitizers.
 
 After that, run ``make`` and ``make test`` as usual.