ScaLAPACK API singletons

[mgates3]

Replaces the internal slate_scalapack_set_target() and similar functions with singletons TargetConfig::value() that query the environment only once. For Target, this also compares the entire string instead of just the 5th character, making it safe from buffer overrun and more robust.

[mgates3]

With some extra debugging output added, we see each MPI rank queries the variables once, and all the variables are correctly passed:

slate> env TEST_LIBS=-lslate_scalapack_api make

slate> setenv SLATE_SCALAPACK_VERBOSE 1
slate> setenv SLATE_SCALAPACK_TARGET HostNest
slate> setenv SLATE_SCALAPACK_IB 32
slate> setenv SLATE_SCALAPACK_PANELTHREADS 4
slate> setenv SLATE_SCALAPACK_LOOKAHEAD 2

slate> mpirun -np 4 test/tester --ref y gesv
% SLATE version 2024.10.29, id 798d22a3
% input: test/tester --ref y gesv
% 2025-01-11 12:34:45, 4 MPI ranks, CPU-only MPI, 4 OpenMP threads per MPI rank
                                                                                                                                                                                         
type  origin  target  gemm     lu  trsm   go   do   A   B       n    nrhs    nb  ib    p    q  la  pt  threshold     error   time (s)       gflop/s  ref time (s)   ref gflop/s  status  
mpi 0: TargetConfig
mpi 0: VerboseConfig
mpi 0: LookaheadConfig
mpi 0: PanelThreadsConfig
mpi 0: IBConfig
mpi 1: TargetConfig
mpi 1: VerboseConfig
mpi 1: LookaheadConfig
mpi 1: PanelThreadsConfig
mpi 1: IBConfig
mpi 2: TargetConfig
mpi 2: VerboseConfig
mpi 2: LookaheadConfig
mpi 2: PanelThreadsConfig
mpi 2: IBConfig
mpi 3: TargetConfig
mpi 3: VerboseConfig
mpi 3: LookaheadConfig
mpi 3: PanelThreadsConfig
mpi 3: IBConfig
scalapack_api/scalapack_gesv.cc:122 slate_pgesv(): target N, verbose 1, la 2, pthreads 4, ib 32, grid_order C
   d    host    task  auto   PPLU  auto  col  row   1   1     100      10   384  32    2    2   1   2       1.00  5.11e-19    0.00522         0.165      0.000686         1.255  pass    
scalapack_api/scalapack_gesv.cc:122 slate_pgesv(): target N, verbose 1, la 2, pthreads 4, ib 32, grid_order C
   d    host    task  auto   PPLU  auto  col  row   1   1     200      10   384  32    2    2   1   2       1.00  5.50e-19   0.000800         7.639      0.000783         7.805  pass    
scalapack_api/scalapack_gesv.cc:122 slate_pgesv(): target N, verbose 1, la 2, pthreads 4, ib 32, grid_order C
   d    host    task  auto   PPLU  auto  col  row   1   1     300      10   384  32    2    2   1   2       1.00  4.00e-19    0.00137        14.418       0.00134        14.796  pass    
scalapack_api/scalapack_gesv.cc:122 slate_pgesv(): target N, verbose 1, la 2, pthreads 4, ib 32, grid_order C
   d    host    task  auto   PPLU  auto  col  row   1   1     400      10   384  32    2    2   1   2       1.00  3.23e-19    0.00460         9.951       0.00323        14.170  pass    
scalapack_api/scalapack_gesv.cc:122 slate_pgesv(): target N, verbose 1, la 2, pthreads 4, ib 32, grid_order C
   d    host    task  auto   PPLU  auto  col  row   1   1     500      10   384  32    2    2   1   2       1.00  2.97e-19    0.00545        16.175       0.00506        17.435  pass    

% Matrix kinds:
%  1: rand, cond unknown

% All tests passed: gesv

With an invalid target, it throws an error:

slate> setenv SLATE_SCALAPACK_TARGET Task    # invalid

slate> mpirun -np 4 ./test/tester --ref y --dim 100 gesv
% SLATE version 2024.10.29, id 27f266f0
% input: ./test/tester --ref y --dim 100 gesv
% 2025-01-11 13:18:48, 4 MPI ranks, CPU-only MPI, 4 OpenMP threads per MPI rank
                                                                                                                                                                                         
type  origin  target  gemm     lu  trsm   go   do   A   B       n    nrhs    nb  ib    p    q  la  pt  threshold     error   time (s)       gflop/s  ref time (s)   ref gflop/s  status  

Error on rank 0: Invalid target: Task in TargetConfig at scalapack_api/scalapack_slate.hh:186. (4 ranks had some error.)
   d    host    task  auto   PPLU  auto  col  row   1   1     100      10   384  32    2    2   1   2       1.00  5.87e-19     0.0359        0.0240            NA            NA  FAILED  

Previously, this would cause a buffer overflow when it accessed targetstr[4].

Invalid ib, lookahead, and panelthreads integers are set to 1:

slate> setenv SLATE_SCALAPACK_TARGET HostTask
slate> setenv SLATE_SCALAPACK_IB 0            # invalid
slate> setenv SLATE_SCALAPACK_LOOKAHEAD 0     # invalid
slate> setenv SLATE_SCALAPACK_PANELTHREADS 0  # invalid

slate> mpirun -np 4 ./test/tester --ref y --dim 100 gesv
% SLATE version 2024.10.29, id 27f266f0
% input: ./test/tester --ref y --dim 100 gesv
% 2025-01-11 13:30:32, 4 MPI ranks, CPU-only MPI, 4 OpenMP threads per MPI rank
                                                                                                                                                                                         
type  origin  target  gemm     lu  trsm   go   do   A   B       n    nrhs    nb  ib    p    q  la  pt  threshold     error   time (s)       gflop/s  ref time (s)   ref gflop/s  status  
scalapack_api/scalapack_gesv.cc:119 slate_pgesv(): target T, verbose 1, la 1, pthreads 1, ib 1, grid_order C
   d    host    task  auto   PPLU  auto  col  row   1   1     100      10   384  32    2    2   1   2       1.00  7.12e-19     0.0129        0.0668      0.000741         1.162  pass    

% Matrix kinds:
%  1: rand, cond unknown

% All tests passed: gesv