Is your feature request related to a problem or challenge?
As noted in #9864 (comment) there might be some optimization available for the substr_index function so to facilitate that add a benchmark for that function.
A new benchmark testing the substr_index function was added in #9878 and available for use to test the performance of that function and any changes.
Describe the solution you'd like
Make the substr_index benchmark faster
To run:
cargo bench --bench substr_index
Describe alternatives you've considered
No response
Additional context
No response