Convert tidy to a non-egg Python package

It seems that servo-tidy is only used by webrender in my GitHub
searches. WebRender could simply use `rustfmt` and the tidy on pypi
hasn't been updated since 2018. Converting tidy to a normal Python
package removes the maintenance burden of continually fixing the easy
install configuration.

Fixes #29094.
Fixes #29334.

python/tidy/tests/lints/invalid_error_tuple.py

@@ -0,0 +1,5 @@
+from servo_tidy.tidy import LintRunner
+
+class Lint(LintRunner):
+    def run(self):
+        yield None

python/tidy/tests/lints/no_lint.py

@@ -0,0 +1,5 @@
+from servo_tidy.tidy import LintRunner
+
+class Linter(LintRunner):
+    def run(self):
+        pass

python/tidy/tests/lints/no_run.py

@@ -0,0 +1,5 @@
+from servo_tidy.tidy import LintRunner
+
+class Lint(LintRunner):
+    def some_method(self):
+        pass

python/tidy/tests/lints/not_inherited.py

@@ -0,0 +1,2 @@
+class Lint(object):
+    pass

python/tidy/tests/lints/proper_file.py

@@ -0,0 +1,6 @@
+from servo_tidy.tidy import LintRunner
+
+class Lint(LintRunner):
+    def run(self):
+        for _ in [None]:
+            yield ('path', 0, 'foobar')