chore(obs): rename ReplicationStats to ReplicationMetricsSnapshot (#6344)

* chore(obs): ReplicationStats -> ReplicationMetricsSnapshot, BucketReplicationStats -> BucketReplicationMetricsSnapshot

Rename in-obs-crate ReplicationStats and BucketReplicationStats to
ReplicationMetricsSnapshot and BucketReplicationMetricsSnapshot respectively.
No serde impact (these types are Prometheus metric collectors, not serialized).
No external consumers found outside the obs crate.

* cleanup: remove #[serial] annotations from e2e_test, scanner, lifecycle, and object-capacity crates

Remove no-op #[serial] attributes (nextest ignores serial_test) and the
serial_test dependency from four crates. All tests already use temp_env
for env-var isolation, making #[serial] purely redundant.

Crates cleaned:
- e2e_test (37 annotations, 9 imports, removed serial_test dep)
- rustfs-scanner (115 annotations across 7 files, removed serial_test dep)
- rustfs-lifecycle (46 annotations, removed serial_test dep)
- rustfs-object-capacity (38 annotations, removed serial_test dep)

Also converted scanner/tests/lifecycle_integration_test.rs
with_forced_immediate_enqueue_timeout helper from unsafe raw
env::set_var/remove_var to temp_env::async_with_vars for proper
isolation, and added async_closure feature to scanner's temp-env dep.

* fix(lifecycle): restore #[serial] on 2 tests that read env vars without temp_env

eval_inner_expires_latest_object_after_days_due and
eval_inner_does_not_panic_on_many_equal_due_events call eval_inner()
which reads ENV_ILM_PROCESS_TIME via std::env::var(). Without #[serial]
they race with other tests that set these vars via temp_env.

* style: cargo fmt

crates/scanner/src/runtime_config.rs

@@ -868,7 +868,6 @@ mod tests {
         SCANNER_CYCLE_MAX_DIRECTORIES, SCANNER_CYCLE_MAX_DURATION, SCANNER_CYCLE_MAX_OBJECTS, SCANNER_DELAY, SCANNER_IDLE_MODE,
         SCANNER_SPEED, SCANNER_SUB_SYS, ScannerSpeed,
     };
-    use serial_test::serial;
     use std::collections::HashMap;
     use std::time::Duration;
     use temp_env::{with_var, with_var_unset};
@@ -916,7 +915,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_uses_persisted_values_when_env_is_unset() {
         let config = server_config_with_scanner(&[
             (SCANNER_SPEED, "slow"),
@@ -944,7 +942,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_normalizes_persisted_default_speed() {
         let config = server_config_with_scanner(&[(SCANNER_SPEED, "default")]);
 
@@ -960,7 +957,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_prefers_env_over_persisted_config() {
         let config = server_config_with_scanner(&[(SCANNER_SPEED, "slowest"), (SCANNER_CYCLE, "600")]);
 
@@ -977,7 +973,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_prefers_heal_bitrot_cycle_over_scanner_compat_config() {
         let config = server_config_with_scanner_and_heal(&[(SCANNER_BITROT_CYCLE, "3600")], &[(HEAL_BITROT_CYCLE, "off")]);
 
@@ -990,7 +985,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_marks_scanner_bitrot_cycle_as_compat_source() {
         let config = server_config_with_scanner(&[(SCANNER_BITROT_CYCLE, "3600")]);
 
@@ -1007,7 +1001,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_normalizes_persisted_default_bitrot_cycles() {
         let default_cycle = DEFAULT_HEAL_BITROT_CYCLE_SECS.to_string();
         for config in [
@@ -1032,7 +1025,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_validation_rejects_invalid_persisted_speed_with_env_override() {
         let config = server_config_with_scanner(&[(SCANNER_SPEED, "warp")]);
 
@@ -1066,7 +1058,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_uses_derived_delay_for_excessive_env_override() {
         let config = server_config_with_scanner(&[(SCANNER_SPEED, "slow")]);
 
@@ -1087,7 +1078,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_status_reports_value_sources() {
         let config = server_config_with_scanner(&[(SCANNER_CYCLE_MAX_OBJECTS, "100"), (SCANNER_CACHE_SAVE_TIMEOUT, "5")]);
 
@@ -1108,7 +1098,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn applied_runtime_config_is_the_authoritative_scheduler_state() {
         let config = server_config_with_scanner(&[(SCANNER_CYCLE, "321")]);
 
@@ -1125,7 +1114,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_status_reports_persisted_pacing_overrides() {
         let config = server_config_with_scanner(&[("delay", "3.5"), ("max_wait", "7")]);
 
@@ -1147,7 +1135,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_status_prefers_env_pacing_overrides() {
         let config = server_config_with_scanner(&[("delay", "3.5"), ("max_wait", "7")]);
 
@@ -1169,7 +1156,6 @@ mod tests {
     }
 
     #[test]
-    #[serial]
     fn scanner_runtime_config_status_preserves_subsecond_max_wait() {
         let config = server_config_with_scanner(&[(SCANNER_SPEED, "fast")]);