rust: tests: drop 'use crate' in bitmap and atomic KUnit tests

rust: tests: drop 'use crate' in bitmap and atomic KUnit tests

The following patch makes usage of macros::kunit_tests crate conditional
on the corresponding configs. When the configs are disabled, compiler
warns on unused crate. So, embed it in unit test declaration.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
Reviewed-by: David Gow <david@davidgow.net>
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260417031531.315281-2-ynorov@nvidia.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>