Figure out PTE convergence issues

[jhp-lanl]

In #383 I added two tests where the PTE solver hadn't been converging. I fixed the issue with the first test, but I have yet to fix the second test.

This is the second test that doesn't converge (I believe with underflow in the temperature):

  GIVEN("Two equations of state") {
    // Set up the three EOS
    constexpr int num_eos = 2;
    std::array<EOS, num_eos> eos_arr;
    // Reference state
    constexpr Real P0 = 1.0e6; // 1 bar
    constexpr Real T0 = 296;   // K
    // Ideal gas air
    constexpr Real rho0_air = 1e-03; // g/cc
    constexpr Real Gruneisen_air = 0.4;
    constexpr Real CV_air = P0 / rho0_air / (Gruneisen_air * T0);
    eos_arr[0] = IdealGas(Gruneisen_air, CV_air);
    // Spiner copper EOS
    constexpr int Cu_matid = 3337;
    const std::string eos_file = "../materials.sp5";
    eos_arr[1] = SpinerEOSDependsRhoT(eos_file, Cu_matid);

    GIVEN("A state that would cause a negative temperature in the PTE solver") {
      // Define the state
      constexpr Real spvol_bulk = 4.010467628234189e-01;
      constexpr Real sie_bulk = 3.290180957185173e+07;
      const std::array<const Real, num_eos> mass_frac = {0.000312273191678158,
                                                         0.999687726808322};

      THEN("The PTE solver should converge") {
        EOS *v_EOS = copy_eos_arr_to_device(num_eos, eos_arr);
        const bool pte_converged =
            run_PTE_from_state(num_eos, v_EOS, spvol_bulk, sie_bulk, mass_frac);
        // TODO: make this test converge
        // CHECK(pte_converged);
        finalize_eos_arr(num_eos, v_EOS);
      }
    }
  }