chore(ecstore): adjudicate 32 bare dead_code allows (#6173)

Replace every bare `#[allow(dead_code)]` in ecstore with either a deletion or a per-item allow carrying a `reason`. Blanket allows at module, struct, and impl level silence the lint for future members too, so each is narrowed to the members that are actually dead.

Delete the dead cluster in `config/heal.rs` (`Config`, its three methods, `RUSTFS_BITROT_CYCLE_IN_MONTHS`, `parse_bitrot_config`) rather than annotate it: it has no callers and is unreachable outside the crate, and `parse_bitrot_config` would panic on its disabled path via `Duration::from_secs_f64(-1.0)`. `DEFAULT_KVS` stays, since the config registry uses it.

Correct two `reason` strings on `Checksum::new` and `PutObjReader::md5_current_hex_string`, which are methods but carried a field-only rationale.

Refs backlog#1823

Co-authored-by: houseme <housemecn@gmail.com>

crates/ecstore/src/services/rebalance/types.rs

@@ -132,7 +132,6 @@ impl RebalanceStopPropagationRecord {
     }
 }
 
-#[allow(dead_code)]
 #[derive(Debug, Clone, Default)]
 pub struct DiskStat {
     pub total_space: u64,

crates/ecstore/src/services/tier/tier_config.rs

@@ -16,8 +16,16 @@ use serde::{Deserialize, Serialize};
 use std::{fmt::Display, io};
 use tracing::info;
 
+#[allow(
+    dead_code,
+    reason = "tier config wire version stamped by the parity constructors below (backlog#1823)"
+)]
 const C_TIER_CONFIG_VER: &str = "v1";
 
+#[allow(
+    dead_code,
+    reason = "tier-name validation message reached only from the parity constructors below (backlog#1823)"
+)]
 const ERR_TIER_NAME_EMPTY: &str = "remote tier name empty";
 const WASABI_US_EAST_ENDPOINT: &str = "https://s3.wasabisys.com";
 const WASABI_ALTERNATIVE_ENDPOINTS: &[(&str, &str)] = &[
@@ -264,7 +272,6 @@ impl Clone for TierConfig {
     }
 }
 
-#[allow(dead_code)]
 impl TierConfig {
     pub(crate) fn clone_with_credentials(&self) -> Self {
         Self {
@@ -284,6 +291,7 @@ impl TierConfig {
         }
     }
 
+    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
     fn endpoint(&self) -> String {
         match self.tier_type {
             TierType::S3 => self.s3.as_ref().map(|s| s.endpoint.clone()).unwrap_or_default(),
@@ -303,6 +311,7 @@ impl TierConfig {
         }
     }
 
+    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
     fn bucket(&self) -> String {
         match self.tier_type {
             TierType::S3 => self.s3.as_ref().map(|s| s.bucket.clone()).unwrap_or_default(),
@@ -322,6 +331,7 @@ impl TierConfig {
         }
     }
 
+    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
     fn prefix(&self) -> String {
         match self.tier_type {
             TierType::S3 => self.s3.as_ref().map(|s| s.prefix.clone()).unwrap_or_default(),
@@ -341,6 +351,7 @@ impl TierConfig {
         }
     }
 
+    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
     fn region(&self) -> String {
         match self.tier_type {
             TierType::S3 => self.s3.as_ref().map(|s| s.region.clone()).unwrap_or_default(),
@@ -457,7 +468,7 @@ impl TierWasabi {
 }
 
 impl TierS3 {
-    #[allow(dead_code)]
+    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
     fn create<F>(
         name: &str,
         access_key: &str,
@@ -528,7 +539,7 @@ pub struct TierMinIO {
 }
 
 impl TierMinIO {
-    #[allow(dead_code)]
+    #[allow(dead_code, reason = "MinIO-parity surface with no caller in this port (backlog#1823)")]
     fn create<F>(
         name: &str,
         endpoint: &str,

crates/ecstore/src/services/tier/tier_gen.rs

@@ -14,7 +14,6 @@
 
 use crate::services::tier::tier::TierConfigMgr;
 
-#[allow(dead_code)]
 impl TierConfigMgr {
     pub fn msg_size(&self) -> usize {
         100