feat(pkg): preserve PostgreSQL types in mapDataType function

* Add support for known PostgreSQL types and modifiers
* Implement canonicalization for PostgreSQL types
* Introduce unit tests for PostgreSQL type handling

pkg/readers/dctx/reader_test.go

@@ -493,3 +493,55 @@ func TestRelationships(t *testing.T) {
 		}
 	}
 }
+
+func TestMapDataType_PostgresTypes(t *testing.T) {
+	reader := &Reader{}
+
+	tests := []struct {
+		name       string
+		inputType  string
+		size       int
+		wantType   string
+		wantLength int
+	}{
+		{
+			name:      "integer array preserved",
+			inputType: "integer[]",
+			wantType:  "integer[]",
+		},
+		{
+			name:      "citext array preserved",
+			inputType: "citext[]",
+			wantType:  "citext[]",
+		},
+		{
+			name:      "vector modifier preserved",
+			inputType: "vector(1536)",
+			wantType:  "vector(1536)",
+		},
+		{
+			name:      "alias canonicalized in array",
+			inputType: "int4[]",
+			wantType:  "integer[]",
+		},
+		{
+			name:       "varchar length from size",
+			inputType:  "varchar",
+			size:       120,
+			wantType:   "varchar",
+			wantLength: 120,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotType, gotLength := reader.mapDataType(tt.inputType, tt.size)
+			if gotType != tt.wantType {
+				t.Fatalf("mapDataType(%q, %d) type = %q, want %q", tt.inputType, tt.size, gotType, tt.wantType)
+			}
+			if gotLength != tt.wantLength {
+				t.Fatalf("mapDataType(%q, %d) length = %d, want %d", tt.inputType, tt.size, gotLength, tt.wantLength)
+			}
+		})
+	}
+}