feat[cartesian]: Introduce default compiler flags

[FlorianDeconinck]

Description

Continuing an ongoing effort to support a wider range of in-use compilers (clang/icx) we introduce a system to detect the C++ compiler and adapt the openmp and compilation flags loaded by default.

We use setuptools to detect the compiler which is future-proofed (3.14) as well as a solution for older python (3.8+).

In order to get a closer match with default Fortran numerics at -O0 we drop all FMA at this optimization level.

Configuration still listens to the GT4PY_* environment variable in priority.

Requirements

• All fixes and/or new features come with corresponding tests.
• Important design decisions have been documented in the appropriate ADR inside the docs/development/ADRs/ folder.

If this PR contains code authored by new contributors please make sure:

• The PR contains an updated version of the AUTHORS.md file adding the names of all the new contributors.