refactor(zerokms): use log target constant instead of string literal

Replace hardcoded "zerokms" target with the ZEROKMS constant from
crate::log for consistency with other logging call sites.

Author: tobyhede

packages/cipherstash-proxy/src/proxy/zerokms/mod.rs

@@ -5,6 +5,7 @@ pub use zerokms::ZeroKms;
 
 use crate::config::TandemConfig;
 use crate::error::{Error, ZeroKMSError};
+use crate::log::ZEROKMS;
 use cipherstash_client::{
     zerokms::{ClientKey, ZeroKMSBuilder},
     AutoStrategy, ZeroKMS,
@@ -20,7 +21,7 @@ pub(crate) fn init_zerokms_client(config: &TandemConfig) -> Result<ZerokmsClient
         .with_workspace_crn(config.auth.workspace_crn.clone())
         .detect()
         .map_err(|e| {
-            tracing::warn!(target: "zerokms", msg = "ZeroKMS authentication strategy detection failed", error = %e);
+            tracing::warn!(target: ZEROKMS, msg = "ZeroKMS authentication strategy detection failed", error = %e);
             ZeroKMSError::AuthenticationFailed
         })?;