refactor: Move clip_tokens function from pr_processing to utils module, and add tests

tests/unittest/test_clip_tokens.py

@@ -0,0 +1,19 @@
+
+# Generated by CodiumAI
+
+import pytest
+
+from pr_agent.algo.utils import clip_tokens
+
+
+class TestClipTokens:
+    def test_clip(self):
+        text = "line1\nline2\nline3\nline4\nline5\nline6"
+        max_tokens = 25
+        result = clip_tokens(text, max_tokens)
+        assert result == text
+
+        max_tokens = 10
+        result = clip_tokens(text, max_tokens)
+        expected_results = 'line1\nline2\nline3\nli...(truncated)'
+        assert result == expected_results