Fix LK catalyst shared object copy for linux/mac only (#947)

### Before submitting

Please complete the following checklist when submitting a PR:

- [ ] All new features must include a unit test.
If you've fixed a bug or added code that should be tested, add a test to
the
      [`tests`](../tests) directory!

- [ ] All new functions and code must be clearly commented and
documented.
If you do make documentation changes, make sure that the docs build and
      render correctly by running `make docs`.

- [ ] Ensure that the test suite passes, by running `make test`.

- [x] Add a new entry to the `.github/CHANGELOG.md` file, summarizing
the
      change, and including a link back to the PR.

- [x] Ensure that code is properly formatted by running `make format`. 

When all the above are checked, delete everything above the dashed
line and fill in the pull request template.


------------------------------------------------------------------------------------------------------------

**Context:**
This is a fix for [this
PR](#945) failing
lightning kokkos build for non-linux systems.

[sc-76296]
**Description of the Change:**

**Benefits:**

**Possible Drawbacks:**

**Related GitHub Issues:**

---------

Co-authored-by: ringo-but-quantum <github-ringo-but-quantum@xanadu.ai>
Co-authored-by: Ali Asadi <10773383+maliasadi@users.noreply.github.com>
Co-authored-by: Amintor Dusko <87949283+AmintorDusko@users.noreply.github.com>

.github/CHANGELOG.md

@@ -119,6 +119,9 @@
 
 ### Bug fixes
 
+* Fix build failure for Lightning-Kokkos editable installation on MacOS due to `liblightning_kokkos_catalyst.so` copy.
+  [(#947)](https://github.com/PennyLaneAI/pennylane-lightning/pull/947)
+
 * Fix missing `liblightning_kokkos_catalyst.so` in Lightning-Kokkos editable installation.
   [(#945)](https://github.com/PennyLaneAI/pennylane-lightning/pull/945)
 

pennylane_lightning/core/_version.py

@@ -16,4 +16,4 @@
    Version number (major.minor.patch[-label])
 """
 
-__version__ = "0.39.0-dev45"
+__version__ = "0.39.0-dev46"

setup.py

@@ -158,9 +158,11 @@ def build_extension(self, ext: CMakeExtension):
 
         # Ensure that catalyst shared object is copied to the build directory for pip editable install
         if backend in ("lightning_kokkos"):
-            source = os.path.join(f"{extdir}", f"lib{backend}_catalyst.so")
-            destination = os.path.join(os.getcwd(), "build")
-            shutil.copy(source, destination)
+            if platform.system() in ["Linux", "Darwin"]:
+                shared_lib_ext = {"Linux": ".so", "Darwin": ".dylib"}[platform.system()]
+                source = os.path.join(f"{extdir}", f"lib{backend}_catalyst{shared_lib_ext}")
+                destination = os.path.join(os.getcwd(), "build")
+                shutil.copy(source, destination)
 
 with open(os.path.join("pennylane_lightning", "core", "_version.py"), encoding="utf-8") as f:
     version = f.readlines()[-1].split()[-1].strip("\"'")