rust: alloc: kvec: simplify KUnit test module name to "rust_kvec"

Remove redundant "_kunit" suffix from test module name.

The naming is now consistent with other Rust components as the test
context is already implied by the #[kunit_tests] macro and test module
location.

Co-developed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
Reviewed-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/r/4eb554c3bf03dd4f9e6dea659497938baab61dba.1753929369.git.zhuhui@kylinos.cn


Signed-off-by: Danilo Krummrich <dakr@kernel.org>