Nightly builds are broken due to new performance library & MKL handling problems

**Describe the bug**
https://cdash.qmcpack.org/index.php?project=QMCPACK

The nightly builds on sulfur, nitrogen and nitrogen2 are broken due to MKL detection isssues... despite the BLAS provider being explicitly requested "-DBLA_VENDOR=OpenBLAS".

This is a new bug and change in behavior. Perhaps it is better to completely skip MKL detection when the BLA_VENDOR is specified and is not MKL/OneAPI.

**Expected behavior**
Builds work as they always have.

**Example failure**

September 15, gcc15-mpi, https://cdash.qmcpack.org/builds/212537/configure

```
"/home/pk7/apps/spack/var/spack/environments/envgccnewmpi/.spack-env/view/bin/cmake" "-DCMAKE_C_COMPILER=mpicc" "-DCMAKE_CXX_COMPILER=mpicxx" "-DENABLE_GCOV:BOOL=false" "-DCMAKE_BUILD_TYPE:STRING=Release" "-DQMC_DATA='/scratch/pk7/QMC_DATA_FULL'" "-DQMC_MPI=1" "-DBUILD_AFQMC=1" "-DENABLE_TIMERS=1" "-DQMC_PERFORMANCE_NIO_MAX_ATOMS=16" "-DQMC_PERFORMANCE_C_GRAPHITE_MAX_ATOMS=16" "-DMPIEXEC_PREFLAGS=--bind-to;none;--oversubscribe" "-DBLA_VENDOR=OpenBLAS" "-DCTEST_USE_LAUNCHERS:BOOL=TRUE" "-GUnix Makefiles" "-S/scratch/pk7/QMCPACK_CI_BUILDS/qmcpack" "-B/scratch/pk7/QMCPACK_CI_BUILDS/build_gccnewmpi"

-- MPI is enabled
-- Looking for posix_memalign
-- Looking for posix_memalign - found
-- Found mkl_core library file. Guessed VPL_ID 'IntelMKL'.
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Could NOT find BLAS (missing: BLAS_LIBRARIES)
CMake Warning at CMake/FindVendorPerfLibs.cmake:203 (message):
Intel mkl_core library file was found. FindBLAS failed most likely when
testing linking MKL for complex reasons.

Threaded MKL requested but linking may fail due to incompatible compiler
OpenMP runtime. To request sequential MKL, set VPL_OMP=OFF.

If you'd like to fully opt out Intel MKL, set VPL_ID=Generic.
Call Stack (most recent call first):
CMake/FindVendorPerfLibs.cmake:366 (find_VPL_core)
CMakeLists.txt:455 (find_package)

-- Could NOT find BLAS (missing: BLAS_LIBRARIES)
-- Could NOT find LAPACK (missing: LAPACK_LIBRARIES)
Reason given by package: LAPACK could not be found because dependency BLAS could not be found.

CMake Warning at CMake/FindVendorPerfLibs.cmake:275 (message):
LAPACK for VPL_lapack_ID 'IntelMKL' with OpenMP ON, not found
Call Stack (most recent call first):
CMake/FindVendorPerfLibs.cmake:369 (find_VPL_lapack)
CMakeLists.txt:455 (find_package)

CMake Error at /home/pk7/apps/spack/var/spack/environments/envgccnewmpi/.spack-env/view/share/cmake-4.2/Modules/FindPackageHandleStandardArgs.cmake:290 (message):
Could NOT find VendorPerfLibs (missing: _vpl_lib_found_ids
VPL_CORE_LIBRARIES LAPACK_LIBRARIES lapack)
Call Stack (most recent call first):
/home/pk7/apps/spack/var/spack/environments/envgccnewmpi/.spack-env/view/share/cmake-4.2/Modules/FindPackageHandleStandardArgs.cmake:654 (_FPHSA_FAILURE_MESSAGE)
CMake/FindVendorPerfLibs.cmake:380 (find_package_handle_standard_args)
CMakeLists.txt:455 (find_package)

-- Configuring incomplete, errors occurred!
CMake Error:
CTEST_USE_LAUNCHERS is enabled, but the RULE_LAUNCH_COMPILE global property
is not defined.
```

It worked correctly on Sept 11. https://cdash.qmcpack.org/builds/211731/configure