Truncate to one empty line in stub files (#7558)

## Summary

This PR modifies a variety of sites in which we insert up to two empty
lines to instead truncate to at most one empty line in stub files. We
already enforce this in _some_ places, but not all.

## Test Plan

`cargo test`

No changes in similarity (as expected, since this only impacts
unformatted `.pyi` files).

Before:

| project | similarity index | total files | changed files |

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1631 |
| django | 0.99983 | 2760 | 36 |
| transformers | 0.99963 | 2587 | 323 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99979 | 3496 | 22 |
| warehouse | 0.99967 | 648 | 15 |
| zulip | 0.99972 | 1437 | 21 |

After:

| project | similarity index | total files | changed files |

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1631 |
| django | 0.99983 | 2760 | 36 |
| transformers | 0.99963 | 2587 | 323 |
| twine | 1.00000 | 33 | 0 |
| typeshed | 0.99979 | 3496 | 22 |
| warehouse | 0.99967 | 648 | 15 |
| zulip | 0.99972 | 1437 | 21 |

crates/ruff_python_formatter/tests/snapshots/format@newlines.pyi.snap

@@ -0,0 +1,311 @@
+---
+source: crates/ruff_python_formatter/tests/fixtures.rs
+input_file: crates/ruff_python_formatter/resources/test/fixtures/ruff/newlines.pyi
+---
+## Input
+```py
+###
+# Blank lines around functions
+###
+
+x = 1
+
+# comment
+
+def f():
+    pass
+
+
+if True:
+    x = 1
+
+# comment
+
+def f():
+    pass
+
+
+x = 1
+
+
+
+# comment
+
+def f():
+    pass
+
+
+x = 1
+
+
+
+# comment
+def f():
+    pass
+
+
+x = 1
+
+# comment
+
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+def f():
+    pass
+
+
+x = 1
+
+
+# comment
+
+
+
+# comment
+
+
+
+def f():
+    pass
+# comment
+
+
+def f():
+    pass
+
+# comment
+
+def f():
+    pass
+
+
+# comment
+
+###
+# Blank lines around imports.
+###
+
+def f():
+    import x
+    # comment
+    import y
+
+
+def f():
+    import x
+
+    # comment
+    import y
+
+
+def f():
+    import x
+    # comment
+
+    import y
+
+
+def f():
+    import x
+    # comment
+
+
+    import y
+
+
+def f():
+    import x
+
+
+    # comment
+    import y
+
+
+def f():
+    import x
+
+    # comment
+
+    import y
+
+
+def f():
+    import x  # comment
+    # comment
+
+    import y
+
+
+def f(): pass  # comment
+# comment
+
+x = 1
+
+
+def f():
+    pass
+
+
+
+
+# comment
+
+x = 1
+```
+
+## Output
+```py
+###
+# Blank lines around functions
+###
+
+x = 1
+
+# comment
+
+def f():
+    pass
+
+if True:
+    x = 1
+
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+
+def f():
+    pass
+
+x = 1
+
+# comment
+# comment
+def f():
+    pass
+
+x = 1
+
+# comment
+
+# comment
+
+def f():
+    pass
+
+# comment
+
+def f():
+    pass
+
+# comment
+
+def f():
+    pass
+
+# comment
+
+###
+# Blank lines around imports.
+###
+
+def f():
+    import x
+
+    # comment
+    import y
+
+def f():
+    import x
+
+    # comment
+    import y
+
+def f():
+    import x
+    # comment
+
+    import y
+
+def f():
+    import x
+    # comment
+
+    import y
+
+def f():
+    import x
+
+    # comment
+    import y
+
+def f():
+    import x
+
+    # comment
+
+    import y
+
+def f():
+    import x  # comment
+    # comment
+
+    import y
+
+def f():
+    pass  # comment
+
+# comment
+
+x = 1
+
+def f():
+    pass
+
+# comment
+
+x = 1
+```
+
+
+