Adopt meson-python install_rpath for runtime library paths

[antonwolfy]

This PR migrates the installed RPATH handling to meson-python's install_rpath argument and raises the minimum build-time meson-python requirement to 0.22.0.

Previously the runtime library search paths were injected as raw -Wl,-rpath,... link_args, which existed only because meson-python < 0.22 ignored the install_rpath argument. meson-python 0.22 (released 2026-09-25) adds first-class install_rpath support and, in the same release, stops preserving the $ORIGIN RPATH that Meson auto-inserts for internal link_with dependencies. The extension modules relied on that auto-inserted entry to locate the co-located libmkl_umath_loops.so, so builds against meson-python 0.22 fail at import time on Linux:

ImportError: libmkl_umath_loops.so: cannot open shared object file: No such file or directory

This surfaced as red test_linux jobs on unrelated PRs (e.g. #273) with no code change, once conda-forge shipped meson-python 0.22.

[antonwolfy]

Blocked on Python 3.10 support — revisit once 3.10 is dropped

The build_linux (3.10, ...) and build_windows (3.10, ...) jobs fail here (all other Python versions pass). Root cause is the meson-python>=0.22.0 floor this PR introduces, not the RPATH change itself:

• install_rpath support (what this PR migrates to) was added in meson-python 0.22.0.
• On conda-forge, meson-python dropped Python 3.10 at 0.21.0 (its depends became python >=3.11); 0.20.0 is the last conda-forge build that supports 3.10. This is a conda-forge packaging decision via the global python_min bump — upstream PyPI 0.22.0 still declares requires-python >=3.10.
• Net: there is no conda-forge meson-python that both builds for Python 3.10 and honors install_rpath, so meson-python>=0.22 cannot be satisfied in the 3.10 build environment. The solver reports the conflict as meson-python >=0.22.0 vs python =3.10 (the _python_rc / 3.14.0rc1 lines in the log are just the solver's noisy hint).

conda-forge dependency floor by version, for reference:

meson-python (conda-forge)	python requirement	install_rpath
0.20.0	>=3.10	no
0.21.0	>=3.11	no
0.22.0	>=3.11	yes

The RPATH change itself is validated: the Linux 3.11+ conda builds produce extension modules with the intended RPATH ($ORIGIN:$ORIGIN/../..:$ORIGIN/../../.. plus the env lib), and both clang build jobs are green.

Plan

Keep this PR open. Revise/merge it once the project drops Python 3.10 (requires-python = ">=3.11" and 3.10 removed from the CI matrices and classifiers) — at that point this clean install_rpath migration with the meson-python>=0.22 floor applies without conflict.