docs: add package godoc and clarify public API

Prepare the extracted library for external consumption with grouped
godoc, extension point docs, and setup requirements. Wire
ErrBadCursorString into decode paths and drop redundant Paginate*Conds
aliases.

Co-authored-by: Cursor <cursoragent@cursor.com>

query_count_test.go

@@ -38,16 +38,16 @@ func TestUsesTupleOrderingEdgeCases(t *testing.T) {
 	assert.False(t, sameCol.UsesTupleOrdering())
 }
 
-func TestPaginateWrapperFuncs(t *testing.T) {
+func TestPaginateCondsValueTypes(t *testing.T) {
 	RegisterColumn(User.ID, Meeting.StartTime)
 
 	intCursor := NewCursor(NewInt64Value(1, User.ID), User.ID, OrderDescending)
-	sql := User.SELECT(User.AllColumns).WHERE(PaginateIntConds(intCursor)).DebugSql()
+	sql := User.SELECT(User.AllColumns).WHERE(PaginateConds(intCursor)).DebugSql()
 	assert.Contains(t, sql, "user.id < 1")
 
 	strCursor := NewCursor(NewStringValue("x", MeetingRoom.ID), MeetingRoom.ID, OrderDescending)
 	RegisterColumn(MeetingRoom.ID)
-	sql = MeetingRoom.SELECT(MeetingRoom.AllColumns).WHERE(PaginateUUIDConds(strCursor)).DebugSql()
+	sql = MeetingRoom.SELECT(MeetingRoom.AllColumns).WHERE(PaginateConds(strCursor)).DebugSql()
 	assert.Contains(t, sql, "meeting_room.id < 'x'")
 
 	tsCursor := NewCursor(
@@ -55,7 +55,7 @@ func TestPaginateWrapperFuncs(t *testing.T) {
 		Meeting.StartTime,
 		OrderDescending,
 	)
-	sql = Meeting.SELECT(Meeting.AllColumns).WHERE(PaginateTimestampConds(tsCursor)).DebugSql()
+	sql = Meeting.SELECT(Meeting.AllColumns).WHERE(PaginateConds(tsCursor)).DebugSql()
 	assert.Contains(t, sql, "meeting.start_time <")
 }
 
@@ -63,6 +63,7 @@ func TestNewCursorFromJSONError(t *testing.T) {
 	RegisterColumn(User.ID)
 	_, err := NewCursorFromJSON(NewInt64Value(0, User.ID), []byte(`{invalid`))
 	require.Error(t, err)
+	require.ErrorIs(t, err, ErrBadCursorString)
 }
 
 func TestColWrongTypePanics(t *testing.T) {