ENH: Meson highs 1.7.x

[HaoZeke]

Should supersede #1405. Draft until:

• It works locally (linux).
• CI passes
• This is checked against SciPy
• Bugfixes from MAINT: pybind11 and the modeling API #1405 are pulled in (as needed)

What's inside (why merge):

• Meson build for highspy (needed for SciPy)
• Minor fixes to reduce warnings, so the following are no longer needed:
  • -Wno-return-type
  • -Wno-switch
  • -Wno-comment
  • -Wno-unused-const-variable
  • -Wno-unused-function

[HaoZeke]

For the windows python issues we might have to wait on mesonbuild/meson#13167

EDIT: No, not really because pybind11 doesn't support this anyway pybind/pybind11#1755

[HaoZeke]

I think, after the conversation with @galabovaa and @jajhall I'll just refocus this to work with SciPy. The Windows build "works" with careful handling of delvewheel but that's about as far as is needed since the team will keep scikit-build as the primary build system.

EDIT: ETA next week.