chore(protocols): drop 43 no-op dead_code allows from swift (#6157)

backlog#1823 step 8, partial. The swift module carries 43 #[allow(dead_code)] attributes, most with a comment naming a consumer: "Used by handler", "Handler integration: GET container", "Used by handler and object.rs".

Every one of them suppresses nothing. crates/protocols/src/lib.rs declares `pub mod swift`, and swift/mod.rs declares all 22 submodules `pub mod`, so every item is publicly reachable and dead_code never applied to it. Removing all 43 leaves the warning count at zero, in both the default and --features swift lanes.

That is also why those comments survived. They assert who calls the item — a claim the compiler normally settles on its own — and the compiler had been silenced by the visibility chain.

The rest of step 8 needs a decision this PR does not make. Downgrading the 22 submodules to `pub(crate) mod` does restore detection, and it surfaces 39 real items, 16 of them the whole of sync.rs: SyncConfig, SyncStatus, SyncQueueEntry, ConflictResolution and every function and constant around them, i.e. Swift container sync is built and never wired.

But the `pub mod` chain is load-bearing. Six integration tests under crates/protocols/tests are separate crates that import the submodules directly (swift::quota, swift::slo, swift::symlink, swift::sync, swift::tempurl, swift::container), and the downgrade fails to compile them. Restoring dead-code detection for this module therefore depends on first deciding whether those tests move in-crate — which is a testing-strategy call, not a cleanup one.

Verification: cargo check -p rustfs-protocols warning-free in the default lane and with --features swift (lib and --tests); clippy --features swift --lib --tests -D warnings clean; cargo nextest run -p rustfs-protocols --features swift 441 passed; make pre-commit exit 0.

Ref rustfs/backlog#1823 (step 8).

crates/protocols/src/swift/router.rs

@@ -50,7 +50,6 @@ pub enum SwiftRoute {
 
 impl SwiftRoute {
     /// Get the account identifier from the route
-    #[allow(dead_code)] // Public API for future use
     pub fn account(&self) -> &str {
         match self {
             SwiftRoute::Account { account, .. } => account,
@@ -60,7 +59,6 @@ impl SwiftRoute {
     }
 
     /// Extract project_id from account string (removes AUTH_ prefix)
-    #[allow(dead_code)] // Public API for future use
     pub fn project_id(&self) -> Option<&str> {
         let account = self.account();
         ACCOUNT_PATTERN