Chore: Upgrade memchr and set edition to 2024

[TAINCER]

Hey, this pr upgrades the memchr crate to 2.8.0, they don't keep a changelog, so I skimmed through the commits from 2.4..=2.8, was only like 2 pages of commits, many CI/Bench commits in there. The tests are passing on my end, seems like there was no breaking change to be api we're using here.

I also set the rust edition to 2024, this threw a warning about some unsafe code:

warning[E0133]: call to unsafe function `std::string::String::as_mut_vec` is unsafe and requires unsafe block
  --> src/io_helpers.rs:45:14
   |
45 |         buf: buf.as_mut_vec(),
   |              ^^^^^^^^^^^^^^^^ call to unsafe function
   |

I wrapped the whole function body in an unsafe block, to fix that. I don't work with unsafe code in my repos on a regular basis, but to my understanding, since this was a unsafe fn before, this shouldn't change behaviour.

[andre-vm]

Hey! Thank you for bringing this up.
I'll take a closer look and merge this as soon as possible.