Code dealing with scanning history messages and extracting some data or
state belongs to avante/history/ so move it there. Along with the move
update the implementation to make use of get_tool_use_data() and
get_tool_result_data() helpers to simplify it.
Also rename the function to History.get_pending_tools() to better
reflect its purpose: "uncalled" means something that was done without
request, unsolicited, not something that has not completed yet.
The utils module has grown too big and contains unrelated functionality.
Start moving code related to managing history messages comprising chat
history into lua/avante/history module to keep the code more manageable.
