format cmake files (#975)

* format cmake files

* update format.sh

* fix linker flags for emscripten

* update readme

* use gersemi

* actual format

* should be public instead of interface

* make test work without download

* simplification

* format

.gersemirc

@@ -0,0 +1,2 @@
+line_length: 80
+indent: 2

.github/workflows/check_format.yml

@@ -22,3 +22,12 @@ jobs:
       with:
         options: "--check --verbose"
         src: "./bindings/python/examples"
+    - uses: actions/setup-python@v5
+      with:
+        python-version: '3.12' 
+        cache: 'pip'
+    - name: "gersemi cmake check"
+      run: |
+        pip3 install gersemi
+        ./scripts/gersemi-check.sh
+