Enforce use of Stable API (Py_LIMITED_API) for C-extension

To modernize MariaDB Connector/Python and eliminate version-specific compilation dependencies, we should enforce the CPython Stable API (Py_LIMITED_API) across the C-extension module.

Currently, enabling Py_LIMITED_API breaks the build in mariadb/mariadb.c due to direct usage of unstable C-struct macros (specifically PyDateTime_IMPORT and <datetime.h> internals). Refactoring these sections to use stable C-API equivalents will allow us to target abi3 and streamline driver distribution.

Motivation

Single Binary Wheel Distribution (abi3):

• Without Py_LIMITED_API, a unique C-extension binary must be built, tested, and shipped for every minor Python release (3.9, 3.10, 3.11, 3.12, 3.13, 3.14, 3.15, etc.).
• With Py_LIMITED_API=0x03090000, a single abi3 wheel per OS/architecture works seamlessly across all current and future CPython 3.9+ releases.

Forward Compatibility & Python 3.15+ Readiness:

• CPython is progressively hiding internal struct representations and deprecating direct C-struct macro access.
• Enforcing Py_LIMITED_API guarantees that the driver strictly relies on public, forward-compatible C-API functions, preventing build breakages on future CPython releases and improving compatibility with free-threaded (No-GIL) runtimes.

CI Efficiency:

• Significantly reduces matrix complexity and build time in automated wheel-building pipelines