Support for open62541 v1.4 series

[ralphlange]

The 1.4 release series of the open62541 project is mature and should be supported.

(We could consider dropping support for the 1.2 series if that simplifies the code somewhere.)

[wtup]

What is the status on this issue?
I've noticed that open62541-1.4 is in the repositories of Debian 13 (trixie) and would make installation of this module easier.

[ralphlange]

No progress yet.

We found that upstream open62541 changed the include file structure in incompatible ways in the 1.4 version.
So, this will require work and testing. For the time being, the convenience argument hasn't been strong enough.