[WIP] Remove adios2.usesteps, set it always to true

This uncovered loads of bugs

include/openPMD/IO/ADIOS/ADIOS2IOHandler.hpp

@@ -229,6 +229,9 @@ class ADIOS2IOHandlerImpl
      * If the iteration encoding is variableBased, we default to using a group
      * table, since it is the only reliable way to recover currently active
      * groups.
+     * If group-based encoding is used without group table, then
+     * READ_RANDOM_ACCESS is forbidden as it will be unreliable in reporting
+     * currently available data.
      */
     IterationEncoding m_iterationEncoding = IterationEncoding::groupBased;
     /**
@@ -1064,7 +1067,7 @@ namespace detail
              *    without steps. This is not a workaround since not using steps,
              *    while inefficient in ADIOS2, is something that we support.
              */
-            NoStream,
+            ReadWithoutStream,
             /**
              * Rationale behind this state:
              * When user code opens a Series, series.iterations should contain
@@ -1152,8 +1155,8 @@ namespace detail
         void create_IO();
 
         void configure_IO(ADIOS2IOHandlerImpl &impl);
-        void configure_IO_Read(std::optional<bool> userSpecifiedUsesteps);
-        void configure_IO_Write(std::optional<bool> userSpecifiedUsesteps);
+        void configure_IO_Read();
+        void configure_IO_Write();
     };
 
 } // namespace detail

include/openPMD/IO/AbstractIOHandler.hpp

@@ -23,6 +23,7 @@
 #include "openPMD/IO/Access.hpp"
 #include "openPMD/IO/Format.hpp"
 #include "openPMD/IO/IOTask.hpp"
+#include "openPMD/IterationEncoding.hpp"
 #include "openPMD/config.hpp"
 
 #if openPMD_HAVE_MPI
@@ -180,6 +181,12 @@ class AbstractIOHandler
 {
     friend class Series;
 
+public:
+    /* @todo access control, remove this from open_file, create_file tasks,
+     *       remove the same field from ADIOS2IOHandlerImpl
+     */
+    IterationEncoding m_encoding = IterationEncoding::groupBased;
+
 private:
     void setIterationEncoding(IterationEncoding encoding)
     {
@@ -193,6 +200,8 @@ class AbstractIOHandler
             // do we really want to have those as const members..?
             *const_cast<Access *>(&m_backendAccess) = Access::CREATE;
         }
+
+        m_encoding = encoding;
     }
 
 public:

include/openPMD/cli/ls.hpp

@@ -110,7 +110,7 @@ namespace cli
             {
                 auto s = Series(
                     argv[1],
-                    Access::READ_ONLY,
+                    Access::READ_LINEAR,
                     R"({"defer_iteration_parsing": true})");
 
                 helper::listSeries(s, true, std::cout);