Allow up to two newlines after trailing clause body comments (#7557)

## Summary

The number of newlines after a trailing comment in a clause body needs
to follow the usual rules -- so, up to two for top-level, up to one for
nested, etc.

For example, Black preserves both newlines after `# comment` here:

```python
if True:
    pass

    # comment


else:
    pass
```

But it truncates to one newline here:

```python
if True:
    if True:
        pass
        # comment


    else:
        pass
else:
    pass
```

## Test Plan

Significant improvement on `transformers`.

Before:

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

|--------------|------------------:|------------------:|------------------:|
| cpython | 0.76083 | 1789 | 1631 |
| django | 0.99983 | 2760 | 36 |
| transformers | 0.99957 | 2587 | 402 |
| 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/resources/test/fixtures/ruff/statement/if.py

@@ -138,6 +138,54 @@ if True:
 else:
     pass
 
+if True:
+    pass
+
+    # comment
+
+else:
+    pass
+
+if True:
+    pass
+
+    # comment
+
+
+else:
+    pass
+
+if True:
+    pass
+
+    # comment
+
+
+
+else:
+    pass
+
+if True:
+    if True:
+        pass
+        # comment
+
+    else:
+        pass
+else:
+    pass
+
+if True:
+    if True:
+        pass
+        # comment
+
+
+    else:
+        pass
+else:
+    pass
+
 # Regression test for https://github.com/astral-sh/ruff/issues/5337
 if parent_body:
     if current_body:

crates/ruff_python_formatter/src/comments/format.rs

@@ -101,9 +101,7 @@ impl Format<PyFormatContext<'_>> for FormatLeadingAlternateBranchComments<'_> {
             } else {
                 last_preceding.end()
             };
-            if lines_after(end, f.context().source()) > 1 {
-                write!(f, [empty_line()])?;
-            }
+            write!(f, [empty_lines(lines_after(end, f.context().source()))])?;
         }
 
         Ok(())

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

@@ -144,6 +144,54 @@ if True:
 else:
     pass
 
+if True:
+    pass
+
+    # comment
+
+else:
+    pass
+
+if True:
+    pass
+
+    # comment
+
+
+else:
+    pass
+
+if True:
+    pass
+
+    # comment
+
+
+
+else:
+    pass
+
+if True:
+    if True:
+        pass
+        # comment
+
+    else:
+        pass
+else:
+    pass
+
+if True:
+    if True:
+        pass
+        # comment
+
+
+    else:
+        pass
+else:
+    pass
+
 # Regression test for https://github.com/astral-sh/ruff/issues/5337
 if parent_body:
     if current_body:
@@ -197,6 +245,7 @@ elif aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa +
 ]:
     ...
 
+
 else:
     ...
 
@@ -305,6 +354,52 @@ if True:
 else:
     pass
 
+if True:
+    pass
+
+    # comment
+
+else:
+    pass
+
+if True:
+    pass
+
+    # comment
+
+
+else:
+    pass
+
+if True:
+    pass
+
+    # comment
+
+
+else:
+    pass
+
+if True:
+    if True:
+        pass
+        # comment
+
+    else:
+        pass
+else:
+    pass
+
+if True:
+    if True:
+        pass
+        # comment
+
+    else:
+        pass
+else:
+    pass
+
 # Regression test for https://github.com/astral-sh/ruff/issues/5337
 if parent_body:
     if current_body: