Allow up to two empty lines after top-level imports (#6777)

## Summary

For imports, we enforce that there's _at least_ one empty line after an
import (assuming the next statement is _not_ an import), but allow up to
two at the module level.

Closes https://github.com/astral-sh/ruff/issues/6760.

## Test Plan

`cargo test`

crates/ruff_python_formatter/resources/test/fixtures/ruff/statement/import.py

@@ -1,3 +1,58 @@
 from a import aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa
 from a import aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa, aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa
 from a import aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa as dfgsdfgsd, aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa as sdkjflsdjlahlfd
+
+# At the top-level, force one empty line after an import, but allow up to two empty
+# lines.
+import os
+import sys
+x = 1
+
+import os
+import sys
+
+x = 1
+
+import os
+import sys
+
+
+x = 1
+
+import os
+import sys
+
+
+
+x = 1
+
+
+# In a nested scope, force one empty line after an import.
+def func():
+    import os
+    import sys
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+
+
+    x = 1

crates/ruff_python_formatter/src/statement/suite.rs

@@ -192,7 +192,19 @@ impl FormatRule<Suite, PyFormatContext<'_>> for FormatSuite {
                     }
                 }
             } else if is_import_definition(preceding) && !is_import_definition(following) {
-                empty_line().fmt(f)?;
+                // Enforce _at least_ one empty line after an import statement (but allow up to
+                // two at the top-level).
+                match self.kind {
+                    SuiteKind::TopLevel => {
+                        match lines_after_ignoring_trivia(preceding.end(), source) {
+                            0 | 1 | 2 => empty_line().fmt(f)?,
+                            _ => write!(f, [empty_line(), empty_line()])?,
+                        }
+                    }
+                    SuiteKind::Function | SuiteKind::Class | SuiteKind::Other => {
+                        empty_line().fmt(f)?;
+                    }
+                }
             } else if is_compound_statement(preceding) {
                 // Handles the case where a body has trailing comments. The issue is that RustPython does not include
                 // the comments in the range of the suite. This means, the body ends right after the last statement in the body.

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

@@ -7,6 +7,61 @@ input_file: crates/ruff_python_formatter/resources/test/fixtures/ruff/statement/
 from a import aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa
 from a import aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa, aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa
 from a import aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa as dfgsdfgsd, aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa as sdkjflsdjlahlfd
+
+# At the top-level, force one empty line after an import, but allow up to two empty
+# lines.
+import os
+import sys
+x = 1
+
+import os
+import sys
+
+x = 1
+
+import os
+import sys
+
+
+x = 1
+
+import os
+import sys
+
+
+
+x = 1
+
+
+# In a nested scope, force one empty line after an import.
+def func():
+    import os
+    import sys
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+
+
+    x = 1
 ```
 
 ## Output
@@ -22,6 +77,59 @@ from a import (
     aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa as dfgsdfgsd,
     aksjdhflsakhdflkjsadlfajkslhfdkjsaldajlahflashdfljahlfksajlhfajfjfsaahflakjslhdfkjalhdskjfa as sdkjflsdjlahlfd,
 )
+
+# At the top-level, force one empty line after an import, but allow up to two empty
+# lines.
+import os
+import sys
+
+x = 1
+
+import os
+import sys
+
+x = 1
+
+import os
+import sys
+
+
+x = 1
+
+import os
+import sys
+
+
+x = 1
+
+
+# In a nested scope, force one empty line after an import.
+def func():
+    import os
+    import sys
+
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+    x = 1
+
+
+def func():
+    import os
+    import sys
+
+    x = 1
 ```