pytest-xdist: pytest in parallel

Require now pytest-xdist from tests/http/requirements.txt and
run pytest in 'auto' parallel mode (counts cpu cores).

For CI runs, set the worker count to 4, overriding the
core count of 2 exposed in the images.

- use Filelock to generate allocated ports at start for all
  workers and have subsequent workers just read the file and
  take the ports for their slot
- make httpd config clearing a function fixture so every test
  starts with a clean httpd config
- have fixture `configures_httpd` as parameter of test cases
  that configure httpd anyway, saving one reload
- add pytest-xdist and filelock to required pyhton modules
- add installs to ruff CI
- give live checks waiting for a server to start up longer time
- add fixtures to tests that rely on a server
- do not stop servers unnecessarily. failures may not start them
  properly again, leading to unexpected fails in whatever follows
- add a https: port to httpd that is *not* back by QUIC to allow
  failover tests without stopping the QUIC server

Closes #17295

tests/http/test_05_errors.py

@@ -37,13 +37,6 @@ log = logging.getLogger(__name__)
                     reason=f"httpd version too old for this: {Env.httpd_version()}")
 class TestErrors:
 
-    @pytest.fixture(autouse=True, scope='class')
-    def _class_scope(self, env, httpd, nghttpx):
-        if env.have_h3():
-            nghttpx.start_if_needed()
-        httpd.clear_extra_configs()
-        httpd.reload()
-
     # download 1 file, check that we get CURLE_PARTIAL_FILE
     @pytest.mark.parametrize("proto", ['http/1.1', 'h2', 'h3'])
     def test_05_01_partial_1(self, env: Env, httpd, nghttpx, proto):
@@ -54,8 +47,8 @@ class TestErrors:
         count = 1
         curl = CurlClient(env=env)
         urln = f'https://{env.authority_for(env.domain1, proto)}' \
-               f'/curltest/tweak?id=[0-{count - 1}]'\
-               '&chunks=3&chunk_size=16000&body_error=reset'
+            f'/curltest/tweak?id=[0-{count - 1}]'\
+            '&chunks=3&chunk_size=16000&body_error=reset'
         r = curl.http_download(urls=[urln], alpn_proto=proto, extra_args=[
             '--retry', '0'
         ])
@@ -71,13 +64,15 @@ class TestErrors:
     def test_05_02_partial_20(self, env: Env, httpd, nghttpx, proto):
         if proto == 'h3' and not env.have_h3():
             pytest.skip("h3 not supported")
+        if proto == 'h3' and env.curl_uses_ossl_quic():
+            pytest.skip("openssl-quic is flaky in yielding proper error codes")
         if proto == 'h3' and env.curl_uses_lib('msh3'):
             pytest.skip("msh3 stalls here")
         count = 20
         curl = CurlClient(env=env)
         urln = f'https://{env.authority_for(env.domain1, proto)}' \
-               f'/curltest/tweak?id=[0-{count - 1}]'\
-               '&chunks=5&chunk_size=16000&body_error=reset'
+            f'/curltest/tweak?id=[0-{count - 1}]'\
+            '&chunks=5&chunk_size=16000&body_error=reset'
         r = curl.http_download(urls=[urln], alpn_proto=proto, extra_args=[
             '--retry', '0', '--parallel',
         ])
@@ -121,7 +116,7 @@ class TestErrors:
         count = 10 if proto == 'h2' else 1
         curl = CurlClient(env=env)
         url = f'https://{env.authority_for(env.domain1, proto)}'\
-                f'/curltest/shutdown_unclean?id=[0-{count-1}]&chunks=4'
+            f'/curltest/shutdown_unclean?id=[0-{count-1}]&chunks=4'
         r = curl.http_download(urls=[url], alpn_proto=proto, extra_args=[
             '--parallel',
         ])