Limit temperature Newton update for multisegment wells

[Copilot]

PR #6816 adds thermal equation solving for MSW but applies the raw Newton update to temperature without any limiting, causing divergence. Pressure already uses sign-preserving clamping to max_pressure_change; temperature needs the same treatment.

Temperature limiting in updateNewton

Before (PR #6816):

value_[seg][Temperature] = old_primary_variables[seg][Temperature] - relaxation_factor * dwells[seg][Temperature];

After:

const int sign = dwells[seg][Temperature] > 0. ? 1 : -1;
const Scalar dx_limited = sign * std::min(std::abs(dwells[seg][Temperature]) * relaxation_factor, max_temperature_change);
value_[seg][Temperature] = std::max(old_primary_variables[seg][Temperature] - dx_limited, Scalar{0.0});

Changes

• MultisegmentWellPrimaryVariables.hpp/cpp — Add enable_energy, Temperature index, update numWellEq = numPhases + 1 + enable_energy. Temperature handled in update(), updateNewton(), copyToWellState(), new getSegmentTemperature() accessor.
• BlackoilModelParameters.hpp/cpp — New MaxTemperatureChangeMsWells parameter (default 5 K, matching the reservoir model's MaxTemperatureChange).
• MultisegmentWellAssemble.hpp — Derive numWellEq from PrimaryVariables instead of duplicating the formula.
• MultisegmentWell_impl.hpp — Pass max_temperature_change through to updateNewton.
• SegmentState.hpp/cpp — Add temperature vector (constructor, serialization, equality).
• Template instantiations (MSWellHelpers.cpp, MultisegmentWellEquations.cpp, WellHelpers.cpp, WellAssemble.cpp) — Add dimensions for numWellEq=5 when energy is enabled.

When enable_energy = false (all non-thermal configurations), numWellEq and all template dimensions are unchanged — zero behavioral difference.

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[GitPaean]

It does not look successful experiment and it should not happen in the main repository. Sorry for the noise.