chore(test): drop field unification experiment

Remove obsolete multifield unification tests from the pre-reset stack.

- Delete `test/dofs/test_field_unification.jl`.

test/dofs/test_field_unification.jl

@@ -1,117 +0,0 @@
-# This file is a part of JuliaFEM.
-# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
-
-"""
-Tests for field type unification.
-
-Tests that field types (Displacement{3}, Temperature, etc.) can be used directly
-in DOF specifications instead of quantity types (Vec{3}, Float64, etc.).
-"""
-
-using Test
-using JuliaFEM
-using Tensors
-
-@testset "Field Type Unification" begin
-    @testset "quantity_type() trait for field types" begin
-        # Test quantity_type trait on field types directly
-        @test quantity_type(Displacement{3}) == Vec{3}
-        @test quantity_type(Displacement{2}) == Vec{2}
-        @test quantity_type(Displacement{1}) == Vec{1}
-        @test quantity_type(Temperature) == Float64
-        @test quantity_type(DisplacementRotation{3}) == Vec{6}
-        @test quantity_type(DisplacementRotation{2}) == Vec{4}
-    end
-
-    @testset "quantity_type() with field types in tuples" begin
-        # Test quantity_type extraction from tuples with field types
-        S_u = @DOFSet{u::DOF{Displacement{3}, Vertex}}
-        @test quantity_type(fieldtype(S_u, :u)) == Vec{3}
-        
-        S_T = @DOFSet{T::DOF{Temperature, Vertex}}
-        @test quantity_type(fieldtype(S_T, :T)) == Float64
-        
-        S_ur = @DOFSet{u::DOF{DisplacementRotation{3}, Vertex}}
-        @test quantity_type(fieldtype(S_ur, :u)) == Vec{6}
-        
-        # Multi-field
-        S_Tu = @DOFSet{
-            T::DOF{Temperature, Vertex},
-            u::DOF{Displacement{3}, Vertex}
-        }
-        @test quantity_type(fieldtype(S_Tu, :T)) == Float64
-        @test quantity_type(fieldtype(S_Tu, :u)) == Vec{3}
-    end
-
-    @testset "DOF counting with field types" begin
-        # Single field: displacement
-        S_u = @DOFSet{u::DOF{Displacement{3}, Vertex}}
-        @test ndofs(Tetrahedron{4}, S_u) == 12  # 4 nodes × 3 components
-        
-        # Single field: temperature
-        S_T = @DOFSet{T::DOF{Temperature, Vertex}}
-        @test ndofs(Tetrahedron{4}, S_T) == 4  # 4 nodes × 1 component
-        
-        # Single field: displacement-rotation
-        S_ur = @DOFSet{u::DOF{DisplacementRotation{3}, Vertex}}
-        @test ndofs(Tetrahedron{4}, S_ur) == 24  # 4 nodes × 6 components
-        
-        # Multi-field: thermo-mechanical
-        S_Tu = @DOFSet{
-            T::DOF{Temperature, Vertex},
-            u::DOF{Displacement{3}, Vertex}
-        }
-        @test ndofs(Tetrahedron{4}, S_Tu) == 16  # 4 + 12
-        
-        # 2D displacement
-        S_u2d = @DOFSet{u::DOF{Displacement{2}, Vertex}}
-        @test ndofs(Triangle{3}, S_u2d) == 6  # 3 nodes × 2 components
-    end
-
-    @testset "Error handling for invalid formats" begin
-        # Test that non-field types in DOF produce errors
-        # Vec{3} is not a field type (should be Displacement{3})
-        S_invalid = @DOFSet{u::DOF{Vec{3}, Vertex}}
-        
-        # This should error because Vec{3} is not a field type (AbstractField)
-        @test_throws ErrorException quantity_type(fieldtype(S_invalid, :u))
-    end
-
-    @testset "field_type_for_dispatch with field types" begin
-        S = @DOFSet{
-            T::DOF{Temperature, Vertex},
-            u::DOF{Displacement{3}, Vertex}
-        }
-        
-        field_T = field_type_for_dispatch(S, :T)
-        @test field_T isa Temperature
-        
-        field_u = field_type_for_dispatch(S, :u)
-        @test field_u isa Displacement{3}
-    end
-
-    @testset "DOF manager with field types" begin
-        using JuliaFEM: DOFManager, _assign_element_dofs!
-        
-        mgr = DOFManager()
-        S = @DOFSet{u::DOF{Displacement{3}, Vertex}}
-        connectivity = (1, 2, 3, 4)  # 4-node tetrahedron
-        
-        dof_indices = _assign_element_dofs!(mgr, S, Tetrahedron{4}, connectivity)
-        
-        # Should return NamedTuple with :u field
-        @test haskey(dof_indices, :u)
-        @test length(dof_indices.u) == 12  # 4 nodes × 3 components
-    end
-
-    @testset "Element creation with field types" begin
-        S = @DOFSet{u::DOF{Displacement{3}, Vertex}}
-        # Element uses flat tuple of UInt64 for dof_indices
-        dof_indices = NTuple{12, UInt64}((1:12...,))
-        elem = Element{Tetrahedron{4}, Lagrange{1}, S}(UInt(1), dof_indices)
-        
-        @test elem isa Element{Tetrahedron{4}, Lagrange{1}, S}
-        @test length(elem.dof_indices) == 12
-    end
-end
-