CI: add same jobs as in original GitHub fork

translate the GitHub CI from the original repo to .gitlab-ci.yml

Note
see .github/workflows/ci.yml

this new CI should run the same tests as in the original fork.

Note
this MR also

• formats the whole workspace with cargo fmt --all in 792ba9cb (see jobs/8238)
• add missing doc introduced by 5d91c12b in 54a094e7 (see jobs/8244)

noticeable differences

• uses the default stable toolchain instead of being explicit
• does not run the build_no_std job (see jobs/8262)

src/kzg10/mod.rs

@@ -422,10 +422,7 @@ where
         }
     }
 
-    pub fn check_hiding_bound(
-        hiding_poly_degree: usize,
-        num_powers: usize,
-    ) -> Result<(), Error> {
+    pub fn check_hiding_bound(hiding_poly_degree: usize, num_powers: usize) -> Result<(), Error> {
         if hiding_poly_degree == 0 {
             Err(Error::HidingBoundIsZero)
         } else if hiding_poly_degree >= num_powers {