<!-- If a section or line item is not applicable, please put `NA` at the end of the line We recommend tracking each non-trivial task as separate issue. To quickly do that, - list your task titles in the list below (it'll become title of the issue later) - after you submit this issue, you can quickly create issues for each task below from description of this issue. Refer to the link below for help. (https://docs.github.com/en/issues/tracking-your-work-with-issues/creating-an-issue#creating-an-issue-from-a-task-list-item) --> Improve function `find_token_metadata_key` in file `cedarling/src/jwt/issuer_index.rs`. To have O(1) search.