Pin library soname by setting SOVERSION in CMake

[SokolovValy]

Problem

Library targets set only VERSION, not SOVERSION:

     set_property(TARGET ${TARGETNAME} PROPERTY VERSION "${PROJECT_VERSION}")                                                                                                             
                                                                                                                                                                                          
 As a result the linker soname contains the full project version, e.g.                                                                                                                    
 `libJKQTPlotter6.so.5.0.0`. Every minor release changes the soname even                                                                                                                  
 though the ABI is compatible, so dependent applications break after a                                                                                                                    
 routine library update.                                                                                                                                                                  

Solution

 Set `SOVERSION` to the project major version. This produces the standard                                                                                                                 
 chain:                                                                                                                                                                                   
                                                                                                                                                                                          
     libJKQTPlotter6.so       (development symlink)                                                                                                                                       
     libJKQTPlotter6.so.5     (soname, stable within major)                                                                                                                               
     libJKQTPlotter6.so.5.0.0 (real file)                                                                                                                                                 
                                                                                                                                                                                          
 Minor releases (5.0.x) now keep the soname `libJKQTPlotter6.so.5` and                                                                                                                    
 dependent binaries load the updated library without relinking.                                                                                                                           
                                                                                                                                                                                          
 The change is applied in `jkqtplotter_setDefaultLibOptions()`, so all                                                                                                                    
 JKQtPlotter libraries get the soname at once.

[Copilot]

Copilot review overview

🟢 Approval recommended

No unresolved review issues were identified.

Review effort: Lite
Findings: None

What changed in this PR

Pins library SONAMEs to the project major version so compatible minor releases do not require relinking.

Changes:

• Sets SOVERSION for all libraries using the shared CMake macro.
• Preserves the full project version via VERSION.

File	Description
cmake/​jkqtplotter_macros.cmake	Adds major-version SONAME configuration.

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