refactor(ecstore): retire set_disk lint blankets via explicit imports (#6697)

refactor(ecstore): retire the set_disk lint blankets by making the prelude explicit

backlog#1823 step 1 / backlog#2029 road 2. Removes the last two module-level lint blankets in ecstore: set_disk/mod.rs #![allow(unused_imports)] and #![allow(unused_variables)], restoring both lints for the whole 40K-line subtree, and deletes the register line for the unused_variables blanket in the same diff (the guard from #6155 is a bidirectional exact match).

The unused_imports blanket existed because 14 submodules consumed mod.rs as a glob prelude (use super::* / use super::super::*), and rustc does not track consumption through glob re-exports. Each glob is now an explicit use super::{...} list, keeping mod.rs as the single import hub while making every import lint-checkable. Names consumed only by test or test-util units carry #[cfg(test)] / #[cfg(all(test, feature = "test-util"))] / #[cfg(any(test, feature = "test-util"))] gates matching their consumers; storage-api traits are routed through the storage_api_contracts facade per the architecture guard.

The sweep then deleted the genuinely dead imports the blanket was hiding (chrono::Utc, glob::Pattern, futures::task::AtomicWaker, rustfs_lock LocalLock, AsyncBatchProcessor, rand::Rng, std::future::Future among others in mod.rs, plus stale scoped imports and one empty test module shell across the subtree). One unused_variables finding surfaced: flush_read_version_coalescer_pending's lane_key is read only by the #[cfg(test)] counter block, handled with the cfg(not(test)) let _ pattern established in #6158.

Verification: cargo check zero warnings versus the 9cf276ed2 baseline on five lanes (default lib / --tests / rio-v2 --tests / test-util --tests / test-util,rio-v2 --tests; the --tests lane keeps the same three pre-existing core/pools.rs and store/object.rs dead-code warnings main already has); clippy --lib --tests -D warnings clean with test-util,rio-v2; cargo nextest run 4567 passed; make pre-commit exit 0.

scripts/ecstore-module-lint-register.txt

@@ -110,4 +110,3 @@ crates/ecstore/src/services/tier/warm_backend_s3.rs|unused_variables
 crates/ecstore/src/services/tier/warm_backend_tencent.rs|clippy::all
 crates/ecstore/src/services/tier/warm_backend_tencent.rs|unused_must_use
 crates/ecstore/src/services/tier/warm_backend_tencent.rs|unused_variables
-crates/ecstore/src/set_disk/mod.rs|unused_variables