rust: Provide and use a workspace.lints table

Provide and use a `workspace.lints` table. This makes it easier to
maintain and to enforce one coding style. Let's explicitly disable the
`missing_docs` linting rule for tests.

MSRV for the lints table is 1.74 [1]

[1] https://doc.rust-lang.org/cargo/reference/workspaces.html#the-lints-table

Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Acked-by: Finn Callies <fcallies@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>

rust/pv_core/src/lib.rs

@@ -1,14 +1,6 @@
 // SPDX-License-Identifier: MIT
 //
 // Copyright IBM Corp. 2023, 2024
-#![deny(missing_docs)]
-#![warn(
-    missing_debug_implementations,
-    trivial_numeric_casts,
-    unstable_features,
-    unused_import_braces,
-    unused_qualifications
-)]
 #![doc = include_str!("../README.md")]
 mod confidential;
 mod error;