Load versioned libz3 soname in Python bindings on Linux (#10290)

The generated Python bindings loaded `libz3.so` without a soversion,
which could bind to an ABI-incompatible shared library when multiple Z3
versions are present. This change makes Linux bindings prefer the
versioned soname while leaving other platforms on the existing lookup
path.

- **Python loader generation**
  - Thread a `z3py_soversion` parameter through `scripts/update_api.py`.
- Generate `_lib_name` as `libz3.so.<major>.<minor>` on Linux, and keep
`libz3.<ext>` elsewhere.
- Reuse `_lib_name` consistently for directory probing, system fallback,
and error messages.

- **Build-system wiring**
- Pass the current `SOVERSION` from the CMake Python bindings build on
Linux.
- Pass the same value through the `mk_make`/`mk_util.py` generation path
so both build systems emit the same loader behavior.

- **In-tree Python bindings layout**
- Add the matching `libz3.so.<major>.<minor>` link in `build/python/` on
Linux so the generated bindings work directly from the build tree.

- **Regression coverage**
- Add a focused script-level test for the generated loader preamble to
check:
    - Linux uses the versioned soname when provided.
- Non-versioned fallback remains available when no soversion is
supplied.

Example of the generated Linux loader behavior:

```python
_sover = '5.0'
_ext = 'so'
_lib_name = 'libz3.%s.%s' % (_ext, _sover) if sys.platform.startswith('linux') and _sover else 'libz3.%s' % _ext
_lib = ctypes.CDLL(_lib_name)
```

<!-- START COPILOT CODING AGENT SUFFIX -->

- Fixes #7518

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>
Co-authored-by: Nikolaj Bjorner <nikolaj@cs.stanford.edu>

scripts/mk_util.py

@@ -3160,6 +3160,7 @@ def mk_bindings(api_files):
         update_api.generate_files(api_files=new_api_files,
           api_output_dir=get_component('api').src_dir,
           z3py_output_dir=get_z3py_dir(),
+          z3py_soversion=f"{VER_MAJOR}.{VER_MINOR}" if is_linux() else None,
           dotnet_output_dir=dotnet_output_dir,
           java_input_dir=java_input_dir,
           java_output_dir=java_output_dir,