Bug/assorted static analysis (#1615)

* Fix failure to return value in `py_mech_cat_value_iterator `.
* String butchered by formatting.
* Join unnecessary separation of string literals in `arborio/cabelio.cpp`
* Add missing throw in s_expr code.
* Return value, not reference, in `merge_iterator::operator++(int)`.
* Check for self-assignment in `mechanism_catalogue`.
* Initialize all members of `mechanism`.
* Fix index check order in `multi_event_stream` debug output.
* Use coordinator_ from base class in `memory::array`.