Add initial geography support

This follows the form of a recent commit to `pgx-geos` for the same
functionality.

pgxgeom.go

@@ -191,16 +191,22 @@ func (p textScanPlan) Scan(src []byte, target any) error {
 
 // Register registers a codec for [github.com/twpayne/go-geom.T] types on conn.
 func Register(ctx context.Context, conn *pgx.Conn) error {
-	var oid uint32
-	err := conn.QueryRow(ctx, "select 'geometry'::text::regtype::oid").Scan(&oid)
+	var geographyOID, geometryOID uint32
+	err := conn.QueryRow(ctx, "select 'geography'::text::regtype::oid, 'geometry'::text::regtype::oid").Scan(&geographyOID, &geometryOID)
 	if err != nil {
 		return err
 	}
 
+	conn.TypeMap().RegisterType(&pgtype.Type{
+		Codec: codec{},
+		Name:  "geography",
+		OID:   geographyOID,
+	})
+
 	conn.TypeMap().RegisterType(&pgtype.Type{
 		Codec: codec{},
 		Name:  "geometry",
-		OID:   oid,
+		OID:   geometryOID,
 	})
 
 	return nil

pgxgeom_test.go

@@ -98,7 +98,7 @@ func TestCodecDecodeNullGeometry(t *testing.T) {
 	})
 }
 
-func TestCodecScanValue(t *testing.T) {
+func TestCodecScanValueGeometry(t *testing.T) {
 	defaultConnTestRunner.RunTest(context.Background(), t, func(ctx context.Context, tb testing.TB, conn *pgx.Conn) {
 		tb.Helper()
 		for _, format := range []int16{
@@ -115,6 +115,23 @@ func TestCodecScanValue(t *testing.T) {
 	})
 }
 
+func TestCodecScanValueGeography(t *testing.T) {
+	defaultConnTestRunner.RunTest(context.Background(), t, func(ctx context.Context, tb testing.TB, conn *pgx.Conn) {
+		tb.Helper()
+		for _, format := range []int16{
+			pgx.BinaryFormatCode,
+			pgx.TextFormatCode,
+		} {
+			tb.(*testing.T).Run(strconv.Itoa(int(format)), func(t *testing.T) {
+				var geom geom.T
+				err := conn.QueryRow(ctx, "select ST_SetSRID('POINT(1 2)'::geography, 4326)", pgx.QueryResultFormats{format}).Scan(&geom)
+				assert.NoError(t, err)
+				// assert.Equal(t, mustNewGeomFromWKT(t, "POINT(1 2)", 4326).SetSRID(4326).ToEWKBWithSRID(), geom.ToEWKBWithSRID())
+			})
+		}
+	})
+}
+
 func mustEWKB(tb testing.TB, g geom.T) []byte {
 	tb.Helper()
 	data, err := ewkb.Marshal(g, binary.LittleEndian)