Merge patch series "cmd/setexpr: support concatenation of direct strings"

Heinrich Schuchardt <heinrich.schuchardt@canonical.com> says:

The setexpr.s command allows to concatenate two strings.

According to the description in doc/usage/cmd/setexpr.rst the parameters
value1 and value2 can be either direct values or pointers to a
memory location holding the values.

Unfortunately `setexpr.s <value1> + <value2>` fails if any of the values
is a direct value. $? is set to false.

* Add support for direct values in setexpr.s.
* Correct the unit test for "setexpr.s fred 0".
* Add a new unit test for "setexpr.s fred '1' + '3'" giving '13'.
* Remove invalid memory leak tests

Link: https://lore.kernel.org/r/20250203151029.60265-1-heinrich.schuchardt@canonical.com