refactor(history): move code collecting pending tools to history

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.