build(dist): each build artifact gets a unique key and merged separately

Uploads are now immutable for actions/upload-artifact@v4.

This gives each build artifact a unique key, and then merges them together at the end.
The [migration guide] suggests this pattern.

[migration guide]: https://github.com/actions/upload-artifact/blob/main/docs/MIGRATION.md#merging-multiple-artifacts

.github/workflows/build.yml

@@ -112,7 +112,7 @@ jobs:
       - name: Archive wheels
         uses: actions/upload-artifact@v4
         with:
-          name: dist
+          name: dist-mac-win
           path: target/wheels/*
 
   build-macos-aarch64:
@@ -164,7 +164,7 @@ jobs:
       - name: Archive wheels
         uses: actions/upload-artifact@v4
         with:
-          name: dist
+          name: dist-macos-aarch64
           path: target/wheels/*
 
   build-manylinux:
@@ -193,7 +193,7 @@ jobs:
       - name: Archive wheels
         uses: actions/upload-artifact@v4
         with:
-          name: dist
+          name: dist-manylinux
           path: target/wheels/*
 
   build-manylinux-aarch64:
@@ -223,7 +223,7 @@ jobs:
       - name: Archive wheels
         uses: actions/upload-artifact@v4
         with:
-          name: dist
+          name: dist-manylinux-aarch64
           path: target/wheels/*
 
   build-sdist:
@@ -249,9 +249,24 @@ jobs:
       - name: Archive wheels
         uses: actions/upload-artifact@v4
         with:
-          name: dist
+          name: dist-sdist
           path: target/wheels/*
-
+
+  merge-build-artifacts:
+    runs-on: ubuntu-latest
+    needs:
+      - build-python-mac-win
+      - build-macos-aarch64
+      - build-manylinux
+      - build-manylinux-aarch64
+      - build-sdist
+    steps:
+      - name: Merge Build Artifacts
+        uses: actions/upload-artifact/merge@v4
+        with:
+          name: dist
+          pattern: dist-*
+
   # NOTE: PyPI publish needs to be done manually for now after release passed the vote
   # release:
   #   name: Publish in PyPI