Add performance measurement tests

[gbrls]

To be able to benchmark this tool's performance when making changes or agains another tool it's necessary to create a suite of tests.

Interesting comparisons:

• kurl vs httpx with the same number of threads (httpx being the baseline for a security tool).
• kurl vs curl (curl being the baseline for http requests).
• kurl with reqwest::blocking vs kurl with tokio.