Clean up rd_grid.cpp some

[eivindjahren]

Add tests for rd_grid.cpp and modernize the for loops that are trivial.

I added tests for all functions that could be added tests for, which was cut short because of #1117 and that there is no simple way of dealing with coarse cells.

Then I very carefully replaced the for loop patterns that could trivially be replaced.

[Copilot]

Pull request overview

Adds unit tests around rd_grid utility/file I/O behavior and modernizes several trivial loop patterns in rd_grid.cpp (mostly scoping loop variables).

Changes:

• Added broad unit tests for regular rectangular grids covering indexing, geometry, keyword allocation, export helpers, and basic file I/O.
• Modernized a number of for loops in rd_grid.cpp (scoped loop indices and some range-based loops).
• Removed a couple of declarations from the public rd_grid.hpp header.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
lib/tests/test_rd_grid.cpp	Adds extensive Catch2 coverage for many rd_grid APIs plus some smoke tests for grid file writing/loading.
lib/resdata/rd_grid.cpp	Refactors multiple loops to modern C++ style (scoped indices / range-based), with no intended behavior change.
lib/include/resdata/rd_grid.hpp	Removes two function declarations from the public header (potential API surface change).

Comments suppressed due to low confidence (1)

lib/resdata/rd_grid.cpp:951

• The range-based loop variable can be const auto &p since p is not modified. This better communicates intent and prevents accidental mutation of corner_list elements.

    for (auto &p : cell->corner_list) {
        if ((p.x == 0) && (p.y == 0)) {
            SET_CELL_FLAG(cell, CELL_FLAG_TAINTED);
            break;
        }
    }

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[SAKavli]

I'm not familiar with C++, what is the purpose of these outer curly braces wrapping the whole loop expressions? Is this some old convention?

[eivindjahren]

It creates a scope for the variables inside it. Its still useful for setting when an object is destructed when using RAII in c++

[SAKavli]

🥓