rust/pv_*: Add more deny lints to pv and pv_core

Denies compiling if one of the following lints find something in pv or
pv_core:
    missing_docs,
    missing_debug_implementations,
    trivial_numeric_casts,
    unstable_features,
    unused_import_braces,
    unused_qualifications

Those lint force developers to avoid unnecessary code and providing
debuggability & documentation for each public symbol.

Fix the compile time error introduced with those lints.

Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>

rust/pv/src/test_utils.rs

@@ -30,7 +30,7 @@ macro_rules! get_test_asset {
 }
 
 pub fn get_cert_asset_path<P: AsRef<Path>>(path: P) -> PathBuf {
-    let mut p = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    let mut p = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
     p.push("tests");
     p.push("assets");
     p.push("cert");