Reject more syntactically invalid Python programs (#8524)

## Summary

This commit adds some additional error checking to the parser such that
assignments that are invalid syntax are rejected. This covers the
obvious cases like `5 = 3` and some not so obvious cases like `x + y =
42`.

This does add an additional recursive call to the parser for the cases
handling assignments. I had initially been concerned about doing this,
but `set_context` is already doing recursion during assignments, so I
didn't feel as though this was changing any fundamental performance
characteristics of the parser. (Also, in practice, I would expect any
such recursion here to be quite shallow since the recursion is done on
the target of an assignment. Such things are rarely nested much in
practice.)

Fixes #6895

## Test Plan

I've added unit tests covering every case that is detected as invalid on
an `Expr`.

crates/ruff_linter/src/rules/eradicate/detection.rs

@@ -163,11 +163,15 @@ mod tests {
             "# ( user_content_type , _ )= TimelineEvent.objects.using(db_alias).get_or_create(",
             &[]
         ));
-        assert!(comment_contains_code(
+        assert!(comment_contains_code("# )", &[]));
+
+        // This used to return true, but our parser has gotten a bit better
+        // at rejecting invalid Python syntax. And indeed, this is not valid
+        // Python code.
+        assert!(!comment_contains_code(
             "#     app_label=\"core\", model=\"user\"",
             &[]
         ));
-        assert!(comment_contains_code("# )", &[]));
 
         // TODO(charlie): This should be `true` under aggressive mode.
         assert!(!comment_contains_code("#def foo():", &[]));

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/yield.py

@@ -22,8 +22,6 @@ def foo():
         pass
 
 
-    (yield a, b) = (1, 2)
-
     # some comment
     for e in l : yield e # some comment
 

crates/ruff_python_formatter/tests/snapshots/format@expression__yield.py.snap

@@ -28,8 +28,6 @@ def foo():
         pass
 
 
-    (yield a, b) = (1, 2)
-
     # some comment
     for e in l : yield e # some comment
 
@@ -151,8 +149,6 @@ def foo():
         # comment
         pass
 
-    (yield a, b) = (1, 2)
-
     # some comment
     for e in l:
         yield e  # some comment