parallelize builds and install nightly cython for free-threaded build

Author: ngoldbaum

.github/workflows/compiler_sanitizers.yml

@@ -61,7 +61,7 @@ jobs:
         pip install -r requirements/test_requirements.txt
     - name: Build
       run:
-        python -m spin build -- -Db_sanitize=address
+        python -m spin build -j2 -- -Db_sanitize=address
     - name: Test
       run: |
         # pass -s to pytest to see ASAN errors and warnings, otherwise pytest captures them
@@ -104,12 +104,14 @@ jobs:
         CONFIGURE_OPTS="--with-thread-sanitizer" pyenv install 3.13t
         pyenv global 3.13t
         echo $PATH
+        # TODO: remove when a released cython supports free-threaded python
+        pip install -i https://pypi.anaconda.org/scientific-python-nightly-wheels/simple cython
         pip install -r requirements/build_requirements.txt
         pip install -r requirements/ci_requirements.txt
         pip install -r requirements/test_requirements.txt
     - name: Build
       run:
-        python -m spin build -- -Db_sanitize=thread
+        python -m spin build -j2 -- -Db_sanitize=thread
     - name: Test
       run: |
         # pass -s to pytest to see TSAN errors and warnings, otherwise pytest captures them