Better agent execution error handling (#54)

A few quality of life improvements around cache handling and repeated tool usage

crewai/agents/exceptions.py

@@ -0,0 +1,20 @@
+from langchain_core.exceptions import OutputParserException
+
+
+class TaskRepeatedUsageException(OutputParserException):
+    """Exception raised when a task is used twice in a roll."""
+
+    error: str = "TaskRepeatedUsageException"
+    message: str = "\nI just used the {tool} tool with input {tool_input}. So I already know the result of that.\n"
+
+    def __init__(self, tool: str, tool_input: str):
+        self.tool = tool
+        self.tool_input = tool_input
+        self.message = self.message.format(tool=tool, tool_input=tool_input)
+
+        super().__init__(
+            error=self.error, observation=self.message, send_to_llm=True, llm_output=""
+        )
+
+    def __str__(self):
+        return self.message