Builder + immutable SparseTable-backed UniformXTabulated2DFunction

[havahol]

This PR splits UniformXTabulated2DFunction into an append-only UniformXTabulated2DFunctionBuilder and an immutable, SparseTable-backed evaluation type, and migrates every call site over to the new split. It targets CPU-work only, and is behaviour preserving.

This PR builds on the four PRs that moved SparseTable/IteratorRange from opm-grid into opm-common (see [1-4]), and is prep work for GPU-porting UniformXTabulated2DFunction and LiveOilPvt in a later PR, the same way Tabulated1DFunction/BrineCo2Pvt were ported. With this PR, porting UniformXTabulated2DFunction to GPU becomes easier as SparseTable is already GPU-ready, in contrast to the std::vector<std::vector<SamplePoint>> data structure originally used.

This PR should be reviewed together with OPM/opm-common#5411

Changes

opm-common

• New opm/material/common/UniformXTabulated2DFunctionBuilder.hpp: carries the old append logic (appendXPos/appendSamplePoint) plus the plain accessors needed by the four PVT classes' initEnd()-style derivation code (xAt/yAt/valueAt/numX/numY). build() && is rvalue-qualified (move-only) and flattens the appended columns into a SparseTable<SamplePoint>, then returns the immutable type via a private constructor.
• Rewrote opm/material/common/UniformXTabulated2DFunction.hpp: samples_ is now a SparseTable<SamplePoint> (default std::vector storage, not GPU-templated yet) instead of std::vector<std::vector<SamplePoint>>. Dropped appendXPos/appendSamplePoint and the old (xPos, yPos, samples) constructor (no external callers); kept the default constructor for .resize(n, Policy) call sites and the operator==/accessors.
• opm/common/utility/IteratorRange.hpp: added front()/back() to iterator_range and mutable_iterator_range — needed for SparseTable-backed row access (yMin/yMax/applies), mirrors the "behaves like a vector of vectors" contract SparseTable already documents.
• Migrated LiveOilPvt, WetGasPvt, DryHumidGasPvt, WetHumidGasPvt: each gets Builder-typed private members for tables that are appended across multiple methods (initFromState, extendPvt*Table_, and the standalone setSaturated* setters used by the manual-PVT-setup path in examples/problems/reservoirproblem.hh), finalized via .build() at the top of initEnd(). Tables built entirely within one function scope (DryHumidGasPvt/WetHumidGasPvt's RWGSALT-derived saturatedWaterVaporizationSaltFactorTable_) use a local Builder instead of a persistent member. WetHumidGasPvt repeats the pattern twice (RvSat and RvwSat pairs).
• tests/material/test_2dtables.cpp: table-construction helpers build via UniformXTabulated2DFunctionBuilder and return std::move(tab).build().

opm-simulators

• opm/simulators/flow/FlowGenericProblem_impl.hpp: rock-compaction tables (rockCompPoroMultWc_/rockCompTransMultWc_) built via a local Builder per region, then .build().
• opm/models/blackoil/blackoilextboparams.cpp: all 10 EXTBO tables (X_, Y_, PBUB_RS_, PBUB_RV_, VISCO_, VISCG_, BO_, BG_, RS_, RV_) built via local Builders, finalized per-region right after that region's construction loop (verified no cross-region reads of an already-finalized table).

Verify

• ctest -R 2dtables (opm-common) — passes, 14 cases.
• eclblackoilpvt (opm-common) — passes, 8 cases. Exercises LiveOilPvt/WetGasPvt/ DryHumidGasPvt/WetHumidGasPvt via the ECL-deck initFromState/extendPvt*Table_/ initEnd path (PVTO/PVTG/PVTGW keywords).
• opmcommon and opmsimulators libraries build clean (no new warnings attributable to these changes).
• reservoir_blackoil_ecfv/reservoir_blackoil_vcfv (opm-simulators) — pass, including the reference-result checksum comparison. These exercise examples/problems/reservoirproblem.hh, the only external caller of LiveOilPvt's standalone setSaturatedOilFormationVolumeFactor/ setSaturatedOilViscosity append path (as opposed to the ECL-deck initFromState path), end to end.
• RockTableTests (opm-common) — passes.
• No serialization/restart or operator== dependency on the touched PVT classes was found in opm-simulators, so this has no restart-format implications.

Stacked dependencies

• [1] Move SparseTable from opm-grid to opm-common opm-common#5404
• [2] Move SparseTable from opm-grid to opm-common #7471
• [3] Move SparseTable from opm-grid to opm-common opm-grid#1071
• [4] Move SparseTable from opm-grid to opm-common opm-upscaling#462