GeezerVison

…2025-59375) (python#139234)

Expose the XML Expat 2.7.2 mitigation APIs to disallow use of
disproportional amounts of dynamic memory from within an Expat
parser (see CVE-2025-59375 for instance).

The exposed APIs are available on Expat parsers, that is,
parsers created by `xml.parsers.expat.ParserCreate()`, as:

- `parser.SetAllocTrackerActivationThreshold(threshold)`, and
- `parser.SetAllocTrackerMaximumAmplification(max_factor)`.

(cherry picked from commit f04bea4)

…on API (python#139366)

Fix some typos left in f04bea4,
and simplify some internal functions to ease maintenance of future
mitigation APIs.

(cherry picked from commit 68a1778)

Idea by @picnixz