Fix RAGFlow cannot start (#16116)

# Summary
- The culprit is commit b4c8711d5 / PR #15415 (fix: upgrade crawl4ai to
0.8.0).
- That upgrade brought in unclecode-litellm, which installs the same
top-level litellm namespace as upstream litellm.
- The crash happens when files from one LiteLLM distribution are mixed
with files from the other: custom_guardrail.py expects
GuardrailTracingDetail, but types/utils.py can come from the older
conflicting package.

pyproject.toml

@@ -210,6 +210,11 @@ constraint-dependencies = [
     # via selenium-wire -> trio-websocket -> trio.
     "trio>=0.26.0",
 ]
+exclude-dependencies = [
+    # crawl4ai>=0.8.6 depends on unclecode-litellm, which installs the same
+    # `litellm` package namespace as upstream litellm and can corrupt imports.
+    "unclecode-litellm",
+]
 override-dependencies = [
     # moodlepy<=0.24.1 pins attrs<23.0.0, but trio>=0.26.0 requires attrs>=23.2.0.
     # attrs 23.x is backward-compatible; moodlepy works fine at runtime with it.