Benchmarks are missing

[zamazan4ik]

Hi!

According to the README, benchmarks can be started with cargo +nightly bench --all-features. However, my output shows that no benchmarks are available in the project.

Information about my env:

• mail-parser version: main branch, a96497d7a39663627207753610f2920910313afc version.
• OS: Fedora 39