Fix #2220: Add validation for numeric model IDs in LLM class

Co-Authored-By: Joe Moura <joao@crewai.com>

tests/unit/test_llm.py

@@ -0,0 +1,21 @@
+import pytest
+
+from crewai.llm import LLM
+
+
+def test_numeric_model_id_validation():
+    # Test with integer model ID
+    with pytest.raises(ValueError, match="Invalid model ID: 3420. Model ID cannot be a numeric value without a provider prefix."):
+        LLM(model=3420)
+    
+    # Test with string numeric model ID
+    with pytest.raises(ValueError, match="Invalid model ID: 3420. Model ID cannot be a numeric value without a provider prefix."):
+        LLM(model="3420")
+    
+    # Test with valid model ID
+    llm = LLM(model="openai/gpt-4")
+    assert llm.model == "openai/gpt-4"
+    
+    # Test with valid model ID that contains numbers
+    llm = LLM(model="gpt-3.5-turbo")
+    assert llm.model == "gpt-3.5-turbo"