[core] expmap performance improvement

[rex-schilasky]

Description

For large maps the update_timestamps function is not performing well.

Changes:

• Utilization of find Function: The find function is used to search for the key k in the _key_to_value map, rather than using at, which would throw an exception if the key is not found.
• Splicing Instead of Erasing and Inserting: Instead of erasing and re-inserting elements into the _key_tracker list, the new version uses the splice function to move the element to the end of the list, improving efficiency.
• Timestamp Update Improvement: The timestamp update logic has been simplified and made more explicit by directly assigning the current time to the timestamp associated with the key k.
• Simplified Clear Functionality: Just clearing the internal map and list without iterating over their elements.

[hannemn]

lgtm as discussed

[github-actions]

clang-tidy made some suggestions

[github-actions]

warning: multiple declarations in a single statement reduces readability [readability-isolate-declaration]

Suggested change

	int run(0), runs(10);
	int run(0);
	int runs(10);