Fix: MPS reader drops RHS/RANGES/BOUNDS entries without a set name

[ZedongPeng]

Summary

The MPS reader assumed the first field of every RHS / RANGES / BOUNDS line is the set name. That field is optional, and Netlib/CUTEst files such as BLEND, SIERRA, GFRD-PNC and DFL001 omit it. On these files the whole RHS section was
silently dropped, so the solver returned OPTIMAL with objective 0 and zero residuals.

The reader now checks whether the first field already names a known row (or column, for BOUNDS); if so there is no set name to skip.

Test

$ ./build/cupdlpx test/BLEND.SIF test/
---------------------------------------------------------------------------------------
                                    cuPDLPx v0.3.0                                    
                        A GPU-Accelerated First-Order LP Solver                        
               (c) Haihao Lu, Massachusetts Institute of Technology, 2025              
---------------------------------------------------------------------------------------
Problem: 74 rows, 83 columns, 491 nonzeros
Settings:
  iter_limit         : 2147483647
  time_limit         : 3600.00 sec
  eps_opt            : 1.0e-04
  eps_feas           : 1.0e-04
  spmv_backend       : cusparseSpMVOp (auto)

Running presolver (PSLP v0.0.8)...
  status          : REDUCED
  presolve time   : 0.000679 sec
  reduced problem : 58 rows, 63 columns, 394 nonzeros

Preconditioning
  Geometric-mean scaling (12 iterations)
  Ruiz scaling (10 iterations)
  Pock-Chambolle scaling (alpha=1.0000)
  Bound-objective scaling
---------------------------------------------------------------------------------------
   runtime     |     objective      |   absolute residuals    |   relative residuals    
  iter   time  |  pr obj    du obj  |  pr res  du res   gap   |  pr res  du res   gap   
---------------------------------------------------------------------------------------
     0 0.0e+00 |  0.0e+00   0.0e+00 | 0.0e+00 0.0e+00 0.0e+00 | 0.0e+00 0.0e+00 0.0e+00 
   200 0.0e+00 | -2.1e+01   0.0e+00 | 9.2e-01 3.6e+00 2.1e+01 | 3.0e-02 2.3e-01 9.5e-01 
   400 8.3e-03 | -2.4e+01  -1.1e+01 | 4.4e-01 2.1e+00 1.4e+01 | 1.4e-02 1.3e-01 3.8e-01 
   600 1.1e-02 | -2.6e+01  -1.6e+01 | 7.5e-01 1.4e+00 1.0e+01 | 2.5e-02 9.0e-02 2.3e-01 
   800 1.3e-02 | -2.7e+01  -2.4e+01 | 1.1e+00 5.5e-01 2.9e+00 | 3.7e-02 3.6e-02 5.6e-02 
  1000 1.6e-02 | -3.2e+01  -2.8e+01 | 1.0e+00 2.6e-01 4.3e+00 | 3.4e-02 1.7e-02 7.0e-02 
  1200 1.8e-02 | -3.4e+01  -3.0e+01 | 9.7e-01 1.0e-01 3.9e+00 | 3.2e-02 6.5e-03 6.0e-02 
  1400 2.1e-02 | -3.1e+01  -3.0e+01 | 2.8e-01 9.3e-02 9.0e-01 | 9.3e-03 6.1e-03 1.5e-02 
  1600 2.3e-02 | -3.3e+01  -3.1e+01 | 3.3e-01 4.5e-02 2.7e+00 | 1.1e-02 2.9e-03 4.2e-02 
  1800 2.6e-02 | -3.1e+01  -3.1e+01 | 1.5e-02 4.4e-02 1.4e-01 | 5.0e-04 2.9e-03 2.2e-03 
  2000 2.8e-02 | -3.2e+01  -3.1e+01 | 1.3e-01 4.0e-02 1.2e+00 | 4.2e-03 2.6e-03 1.8e-02 
  2200 3.0e-02 | -3.2e+01  -3.1e+01 | 1.5e-01 1.3e-02 9.6e-01 | 5.0e-03 8.4e-04 1.5e-02 
  2400 3.3e-02 | -3.1e+01  -3.1e+01 | 5.7e-02 7.2e-03 7.1e-02 | 1.9e-03 4.7e-04 1.1e-03 
  2600 3.5e-02 | -3.1e+01  -3.1e+01 | 4.8e-02 6.4e-03 3.5e-01 | 1.6e-03 4.2e-04 5.6e-03 
  2800 3.7e-02 | -3.1e+01  -3.1e+01 | 2.4e-02 4.5e-03 7.2e-02 | 8.0e-04 2.9e-04 1.1e-03 
  3000 4.0e-02 | -3.1e+01  -3.1e+01 | 2.3e-02 2.2e-03 9.7e-02 | 7.4e-04 1.4e-04 1.6e-03 
  3200 4.2e-02 | -3.1e+01  -3.1e+01 | 6.8e-03 1.5e-03 5.3e-03 | 2.3e-04 9.9e-05 8.5e-05 
  3400 4.5e-02 | -3.1e+01  -3.1e+01 | 1.4e-02 8.1e-04 9.5e-02 | 4.8e-04 5.3e-05 1.5e-03 
  3600 4.7e-02 | -3.1e+01  -3.1e+01 | 1.1e-02 4.1e-05 8.2e-02 | 3.6e-04 2.7e-06 1.3e-03 
  3800 5.0e-02 | -3.1e+01  -3.1e+01 | 2.6e-04 2.3e-04 7.2e-04 | 8.7e-06 1.5e-05 1.2e-05 
---------------------------------------------------------------------------------------
Solution Summary
  Status                 : OPTIMAL
  Presolve time          : 0.000679 sec
  Precondition time      : 0.003345 sec
  Solve time             : 0.0521 sec
  Iterations             : 3800
  Primal objective       : -30.81058612
  Dual objective         : -30.80986236
  Objective gap          : 1.156e-05
  Primal infeas          : 8.746e-06
  Dual infeas            : 1.498e-05