Ported setup.py to pyproject.toml (#2555)

* Ported setup.py to pyproject.toml, refs #2553

* Make fixtures tests less flaky

The in-memory fixtures table was being shared between different
instances of the test client, leading to occasional errors when
running the full test suite.

.github/workflows/publish.yml

@@ -20,7 +20,7 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
         cache: pip
-        cache-dependency-path: setup.py
+        cache-dependency-path: pyproject.toml
     - name: Install dependencies
       run: |
         pip install -e '.[test]'
@@ -41,7 +41,7 @@ jobs:
       with:
         python-version: '3.13'
         cache: pip
-        cache-dependency-path: setup.py
+        cache-dependency-path: pyproject.toml
     - name: Install dependencies
       run: |
         pip install setuptools wheel build
@@ -62,7 +62,7 @@ jobs:
       with:
         python-version: '3.10'
         cache: pip
-        cache-dependency-path: setup.py
+        cache-dependency-path: pyproject.toml
     - name: Install dependencies
       run: |
         python -m pip install -e .[docs]