Move token related functions to common (#10942)

### What problem does this PR solve?

As title

### Type of change

- [x] Refactoring

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

graphrag/general/community_reports_extractor.py

@@ -21,7 +21,7 @@ from graphrag.general.extractor import Extractor
 from graphrag.general.leiden import add_community_info2graph
 from rag.llm.chat_model import Base as CompletionLLM
 from graphrag.utils import perform_variable_replacements, dict_has_keys_with_types, chat_limiter
-from rag.utils import num_tokens_from_string
+from common.token_utils import num_tokens_from_string
 import trio