fix: Python wheel build fails due to Intel MKL repository deprecation and static linking default

[LHT129]

Problem

The Python wheel build (make pyvsag) is failing both locally and in CI on the main branch.

1. Local Build Failure

After commit 3897bb4c (modernize python build system), the build fails with:

CMake Error at extern/mkl/mkl.cmake:40 (message):
  Could not find Intel MKL (static) or OpenMP libraries/headers.

Root cause: The new setup.py defaults MKL_STATIC_LINK=ON, but most systems only have dynamic MKL libraries (libiomp5.so, libmkl_rt.so), not static libraries (libiomp5.a, libmkl_core.a).

2. CI Build Failure

The CI workflow build_release_wheel.yml consistently fails on main branch with:

Could not fetch/save url https://yum.repos.intel.com/mkl/setup/intel-mkl.repo
No package intel-mkl-64bit-2020.0-088 available.

Root cause: Intel's MKL yum repository has been deprecated/removed. The GPG key URL and package repo are no longer accessible.

Evidence

• CI runs on main: https://github.com/alibaba/vsag/actions/workflows/build_release_wheel.yml - all recent runs show failure
• Local system has libiomp5.so but not libiomp5.a
• Intel MKL repo URLs return certificate/validation errors

Affected Files

• python/setup.py - defaults to MKL_STATIC_LINK=ON without ENABLE_INTEL_MKL option
• python/pyproject.toml - tries to install MKL from deprecated Intel yum repo
• scripts/deps/install_deps_centos.sh - same deprecated MKL installation logic

Potential Solutions

1. Change default to dynamic linking: Set MKL_STATIC_LINK=OFF by default in setup.py
2. Use OpenBLAS for CI: Set ENABLE_INTEL_MKL=OFF and install openblas-devel instead of MKL
3. Alternative MKL source: Use system packages like libmkl-dev (apt) if available

Priority

High - This blocks all Python wheel releases on PyPI.

[wxyucs]

fix in #1806