feat(libmeanfield): centrifugal + pressure

libmeanfield/interface/solver/fields.cppm

@@ -0,0 +1,29 @@
+module;
+
+#include <cstdint>
+
+export module mean_field:solver.fields;
+
+export namespace mean_field::solver {
+    enum class FieldBlock : std::uint8_t {
+        velocity          = 0,
+        density           = 1,
+        gravity_gradient  = 2,
+        gravity_potential = 3,
+        displacement      = 4,
+        count             = 5
+    };
+
+    [[nodiscard]] constexpr int block_index(const FieldBlock field) noexcept {
+        return static_cast<int>(field);
+    }
+
+    inline constexpr int field_block_count = block_index(FieldBlock::count);
+
+    static_assert(block_index(FieldBlock::velocity) == 0);
+    static_assert(block_index(FieldBlock::density) == 1);
+    static_assert(block_index(FieldBlock::gravity_gradient) == 2);
+    static_assert(block_index(FieldBlock::gravity_potential) == 3);
+    static_assert(block_index(FieldBlock::displacement) == 4);
+    static_assert(field_block_count == 5);
+} // namespace mean_field::solver