chore(io-metrics): remove the zero-consumer config module (391 lines) (#6008)

crates/io-metrics/src/config.rs was a near-copy of io-core's Backpressure/Deadlock configuration with already-drifted field names (high_watermark vs io-core's high_water_mark) and had no consumer outside the crate's own example: the canonical BackpressureConfig lives in crates/io-core/src/backpressure.rs. Delete the module, its lib.rs re-exports, and the example's unified-config section, and settle the corresponding ARCHITECTURE.md ledger line that tracked this copy's removal.

Ref rustfs/backlog#1833 (PR4).

crates/io-metrics/examples/metrics_example.rs

@@ -14,9 +14,7 @@
 
 //! Example demonstrating metrics and configuration usage.
 
-use rustfs_io_metrics::{
-    AccessTracker, AdaptiveTTL, CacheConfig, CacheSettings, IoConfig, IoSchedulerSettings, record_cache_size,
-};
+use rustfs_io_metrics::{AccessTracker, AdaptiveTTL, CacheConfig, record_cache_size};
 use std::time::Duration;
 
 fn main() {
@@ -32,7 +30,6 @@ fn main() {
     access_tracker_example();
 
     // 4. Unified configuration example
-    unified_config_example();
 
     // 5. Metrics recording example
     metrics_recording_example();
@@ -109,26 +106,6 @@ fn access_tracker_example() {
     println!();
 }
 
-fn unified_config_example() {
-    println!("--- Unified Configuration ---");
-
-    let config = IoConfig::new()
-        .with_cache(
-            CacheSettings::new()
-                .with_max_capacity(5000)
-                .with_ttl(Duration::from_secs(600)),
-        )
-        .with_scheduler(IoSchedulerSettings::new().with_max_concurrent_reads(64));
-
-    println!("  Cache capacity: {}", config.cache.max_capacity);
-    println!("  Cache TTL: {:?}", config.cache.default_ttl);
-    println!("  Max concurrent reads: {}", config.scheduler.max_concurrent_reads);
-    println!("  Backpressure high watermark: {}", config.backpressure.high_watermark);
-    println!("  Default timeout: {:?}", config.timeout.default_timeout);
-
-    println!();
-}
-
 fn metrics_recording_example() {
     println!("--- Metrics Recording ---");