unittests: migrate from jsonschema to fastjsonschema

The former has rust dependencies, which lead to max capping on Cygwin
since there is no rust compiler there. But it turns out there are other
disadvantages of jsonschema:

- it involves installing 5 wheels, instead of just 1
- it is much slower

To give some perspective to the latter issue, this is what it looks like
when I test with jsonschema:

```
===== 1 passed, 509 deselected in 3.07s =====
Total time: 3.341 seconds
```

And here's what it looks like when I test with fastjsonschema:
```
===== 1 passed, 509 deselected, 1 warning in 0.28s =====
Total time: 0.550 seconds
```

I cannot think of a good reason to use the former. Although in order to
work on old CI images, we'll support it as a fallback mechanism

.github/workflows/cygwin.yml

@@ -76,8 +76,7 @@ jobs:
       - name: Run pip
         run: |
           export PATH=/usr/bin:/usr/local/bin:$(cygpath ${SYSTEMROOT})/system32
-          # jsonschema is max capped because the new version depends on rust dependencies which are... hard to get on cygwin
-          python3 -m pip --disable-pip-version-check install gcovr 'jsonschema<4.18' pefile pytest pytest-subtests pytest-xdist coverage
+          python3 -m pip --disable-pip-version-check install gcovr fastjsonschema pefile pytest pytest-subtests pytest-xdist coverage
         shell: C:\cygwin\bin\bash.exe --noprofile --norc -o igncr -eo pipefail '{0}'
 
       - uses: actions/cache/save@v3

.github/workflows/macos.yml

@@ -33,7 +33,7 @@ jobs:
         python-version: '3.x'
     - run: |
         python -m pip install --upgrade pip
-        python -m pip install pytest pytest-xdist pytest-subtests jsonschema coverage
+        python -m pip install pytest pytest-xdist pytest-subtests fastjsonschema coverage
     - run: brew install pkg-config ninja llvm qt@5
     - env:
         CPPFLAGS: "-I/usr/local/include"

.github/workflows/msys2.yml

@@ -80,7 +80,7 @@ jobs:
             mingw-w64-${{ matrix.MSYS2_ARCH }}-python-lxml
             mingw-w64-${{ matrix.MSYS2_ARCH }}-python-setuptools
             mingw-w64-${{ matrix.MSYS2_ARCH }}-python-pip
-            mingw-w64-${{ matrix.MSYS2_ARCH }}-python-jsonschema
+            mingw-w64-${{ matrix.MSYS2_ARCH }}-python-fastjsonschema
             mingw-w64-${{ matrix.MSYS2_ARCH }}-${{ matrix.TOOLCHAIN }}
 
       - name: Install dependencies
@@ -100,7 +100,7 @@ jobs:
       - name: Run Tests
         run: |
           if [[ "${{ matrix.MSYS2_ARCH }}" == "x86_64" ]]; then
-            # There apparently is no clean way to add to the PATH in the 
+            # There apparently is no clean way to add to the PATH in the
             # previous step?
             # See for instance https://github.com/msys2/setup-msys2/issues/171
             export PATH=$PATH:$PWD/pypy3local

ci/ciimage/common.sh

@@ -15,7 +15,7 @@ base_python_pkgs=(
   pytest-xdist
   pytest-subtests
   coverage
-  jsonschema
+  fastjsonschema
 )
 
 python_pkgs=(

ci/run.ps1

@@ -92,7 +92,7 @@ python --version
 
 # Needed for running unit tests in parallel.
 echo ""
-python -m pip --disable-pip-version-check install --upgrade pefile pytest-xdist pytest-subtests jsonschema coverage
+python -m pip --disable-pip-version-check install --upgrade pefile pytest-xdist pytest-subtests fastjsonschema coverage
 
 # Needed for running the Cython tests
 python -m pip --disable-pip-version-check install cython

unittests/internaltests.py

@@ -1012,19 +1012,30 @@ class InternalTests(unittest.TestCase):
     def test_validate_json(self) -> None:
         """Validate the json schema for the test cases."""
         try:
-            from jsonschema import validate, ValidationError
+            from fastjsonschema import compile, JsonSchemaValueException as JsonSchemaFailure
+            fast = True
         except ImportError:
-            if is_ci():
-                raise
-            raise unittest.SkipTest('Python jsonschema module not found.')
-
-        schema = json.loads(Path('data/test.schema.json').read_text(encoding='utf-8'))
+            try:
+                from jsonschema import validate, ValidationError as JsonSchemaFailure
+                fast = False
+            except:
+                if is_ci():
+                    raise
+                raise unittest.SkipTest('neither Python fastjsonschema nor jsonschema module not found.')
+
+        with open('data/test.schema.json', 'r', encoding='utf-8') as f:
+            data = json.loads(f.read())
+
+        if fast:
+            schema_validator = compile(data)
+        else:
+            schema_validator = lambda x: validate(x, schema=data)
 
         errors: T.List[T.Tuple[Path, Exception]] = []
         for p in Path('test cases').glob('**/test.json'):
             try:
-                validate(json.loads(p.read_text(encoding='utf-8')), schema=schema)
-            except ValidationError as e:
+                schema_validator(json.loads(p.read_text(encoding='utf-8')))
+            except JsonSchemaFailure as e:
                 errors.append((p.resolve(), e))
 
         for f, e in errors: