fix(ecstore): default rename fanout to parallel early-ack path (#6443)

* feat(allocator): replace mimalloc/libmimalloc-sys with rustfs-mimalloc/rustfs-mimalloc-sys

Replace the upstream xonatius/mimalloc_rust.git fork (mimalloc + libmimalloc-sys)
with the published rustfs-mimalloc (v0.5.0) and rustfs-mimalloc-sys (v0.5.0) crates
from crates.io.

The new crates are based on mimalloc V3 (v3.5.0) and provide:
- MiMalloc global allocator with safe API (collect, stats_json, process_info)
- Heap management and arena operations (heap module)
- Full FFI bindings to mimalloc V3

Changes:
- Workspace deps: mimalloc + libmimalloc-sys (git) → rustfs-mimalloc + rustfs-mimalloc-sys (crates.io)
- allocator_reclaim.rs: libmimalloc_sys::mi_collect → rustfs_mimalloc::MiMalloc::collect
- memory_observability.rs: raw FFI mi_stats_get_json → MiMalloc::stats_json()
- main.rs: heap ownership tests use Heap::contains() (V3 API)
- deny.toml: remove xonatius/mimalloc_rust.git from allow-git

Co-Authored-By: heihutu <heihutu@gmail.com>

* fix(ecstore): default rename fanout to parallel early-ack path

Switch the default rename_data commit fanout from serial join_all to the
parallel JoinSet early-ack path. The serial path (#5987) was the primary
cause of the 1MiB PUT regression (-71.7%) observed in rc.3 benchmarks.

A/B verification on testing 4-node cluster (c=64, 1MiB PUT, 2min):
  - Serial (join_all):     96.99 MiB/s, P50=644ms
  - Early ack (JoinSet):  177.46 MiB/s, P50=407ms  (+83%)

Also:
- Update rename_data_reclaims_synthetic_inline_rollback_dir_after_commit
  to use rename_data_owned and await tail_drain for proper cleanup.
- Update rename_data_waits_for_tail_disk_after_write_quorum to explicitly
  test the serial path (now non-default) via env override.
- Add error source chain to HTTP Body stream transport error log
  (backlog#2005) so the underlying cause is visible.

Ref: rustfs/backlog#2005
Ref: rustfs/backlog#1792#issuecomment-5384346238
Ref: rustfs/backlog#1792#issuecomment-5384370938

Co-Authored-By: heihutu <heihutu@gmail.com>

---------

Co-authored-by: heihutu <heihutu@gmail.com>

rustfs/src/server/http.rs

@@ -1831,6 +1831,13 @@ fn handle_connection_error(peer_addr: Option<&str>, err: &(dyn std::error::Error
         } else if hyper_err.is_parse() {
             log_transport_failed(peer_addr, "parse_failure", &hyper_err.to_string());
         } else if hyper_err.is_user() {
+            // is_user() = "error from user's Body stream": the application
+            // returned a streaming body that failed mid-flight. Log the full
+            // error source chain so the underlying cause (disk read failure,
+            // upstream RPC error, deleted object, etc.) is visible.
+            let cause = std::error::Error::source(hyper_err)
+                .map(|e| e.to_string())
+                .unwrap_or_default();
             error!(
                 event = EVENT_HTTP_TRANSPORT_FAILED,
                 component = LOG_COMPONENT_SERVER,
@@ -1838,6 +1845,7 @@ fn handle_connection_error(peer_addr: Option<&str>, err: &(dyn std::error::Error
                 peer_addr = %peer_addr,
                 error_kind = "service_error",
                 error = %hyper_err,
+                cause = %cause,
                 result = "transport_error",
                 "HTTP transport failed"
             );