fix: suppress dead code warnings in cache_info.rs

The unittests here rely on the cfg(not(test)) antipattern for mocking,
which new rust compiler interprets as the production version of the
structs being dead-code when running unittests.

Refactoring this to eliminate mocking is difficult, because fdt unit
tests rely on the mocks removing all host-specific information from the
cpu FDT nodes (particularly cache information, which in prod is read
from the host sysfs, but in test mode is some dummy mock values).

Signed-off-by: Patrick Roy <[email protected]>

src/vmm/src/arch/aarch64/cache_info.rs

@@ -32,6 +32,7 @@ trait CacheStore: std::fmt::Debug {
 }
 
 #[derive(Debug)]
+#[cfg_attr(test, allow(unused))]
 pub(crate) struct CacheEntry {
     // Cache Level: 1, 2, 3..
     pub level: u8,
@@ -206,6 +207,7 @@ impl CacheType {
     }
 }
 
+#[cfg_attr(test, allow(unused))]
 fn readln_special<T: AsRef<Path>>(file_path: &T) -> Result<String, CacheInfoError> {
     let line = fs::read_to_string(file_path)?;
     Ok(line.trim_end().to_string())