Add HIRES (Bari IVP set) work-precision example for STIFF3

[Copilot]

This PR adds the HIRES benchmark from the University of Bari IVP test set as a new STIFF3 example. It adapts the published ODE/Jacobian/IC/final-time definition and adds an eps sweep study that emits gnuplot-ready CPU-time vs tolerance data.

• HIRES example implementation

  • Added example/hires.f90 with:
    • 8D HIRES RHS (fun) and analytic Jacobian (jac)
    • Bari initial condition and final time t = 321.8122
    • Reference-solution check at final time against published values

• Work-precision study output

  • Added tolerance sweep over eps = [1e-4, 1e-5, 1e-6, 1e-7, 1e-8, 1e-9]
  • Writes hires_work_precision.dat for gnuplot with columns:
    • eps cpu_time_seconds max_relative_error nfev njev nlu nsol nacc nrej
  • Purpose: plot CPU time (y) vs error tolerance eps (x)

• Build/docs integration

  • Registered hires in example/CMakeLists.txt
  • Updated README example list and HIRES output description

real(wp), parameter :: eps_values(ncases) = [ &
  1.0e-4_wp, 1.0e-5_wp, 1.0e-6_wp, 1.0e-7_wp, 1.0e-8_wp, 1.0e-9_wp ]
...
call write_gnuplot_data('hires_work_precision.dat', eps_values, cpu_times, errors, stats)