MFEM 4.9.1 prep

[sshiraiwa]

This PR include

• Requires SWIG >= 4.4.
• Added git_is_tracking_remote in build_util, which is called before git pull.
• pgridfunc.i is adjusted to deal with an error caused by
  mfem::ParGridFunction::ProjectDiscCoefficient(std::variant<mfem::Coefficient*, mfem::VectorCoefficient*>)
  which was introduced recently in pgridfunc.hpp
• fe_pyramid.i is added
• increment version number to 4.9.1

[sshiraiwa]

Made PR to trigger build test actions

[Copilot]

🟡 Changes recommended

The new fe_pyramid extensions are built but not re-exported via the high-level mfem.ser / mfem.par convenience modules, and the Python version classifier change appears inconsistent with current CI coverage.

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Pull request overview

Prepares PyMFEM for the 4.9.1 release by updating package metadata/versioning and adding new SWIG bindings for MFEM’s pyramid finite element header in both serial and parallel builds.

Changes:

• Add fe_pyramid SWIG interface modules and wire them into the SWIG build lists for _ser and _par.
• Import the new SWIG interface from the existing fe.i aggregation modules.
• Update project metadata (Python classifiers) and bump mfem.__version__ to 4.9.1, with a changelog entry.

File summaries

File	Description
pyproject.toml	Updates supported-Python classifiers (adds 3.14, drops 3.9).
mfem/_ser/setup.py	Adds fe_pyramid to the serial extension build module list.
mfem/_ser/fe.i	Imports the new fe_pyramid.i interface into the serial FE aggregation.
mfem/_ser/fe_pyramid.i	New serial SWIG module wrapping fem/fe/fe_pyramid.hpp (guarded by header-exists macro).
mfem/_par/setup.py	Adds fe_pyramid to the parallel extension build module list.
mfem/_par/fe.i	Imports the new fe_pyramid.i interface into the parallel FE aggregation.
mfem/_par/fe_pyramid.i	New parallel SWIG module wrapping fem/fe/fe_pyramid.hpp (guarded by header-exists macro).
mfem/init.py	Bumps __version__ to 4.9.1.
docs/changelog.txt	Notes the addition of fe_pyramid.i.

Review details

• Files reviewed: 9/9 changed files
• Comments generated: 3
• Review effort level: Lite

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