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/account.rs

@@ -38,7 +38,6 @@ use std::collections::HashMap;
 /// - Account format is invalid
 /// - Credentials don't contain project_id
 /// - Account project_id doesn't match credentials project_id
-#[allow(dead_code)] // Used by Swift implementation
 pub fn validate_account_access(account: &str, credentials: &Credentials) -> SwiftResult<String> {
     // Extract project_id from account (strip "AUTH_" prefix)
     let account_project_id = account
@@ -70,7 +69,6 @@ pub fn validate_account_access(account: &str, credentials: &Credentials) -> Swif
 ///
 /// Admin users (with "admin" or "reseller_admin" roles) can perform
 /// cross-tenant operations and administrative tasks.
-#[allow(dead_code)] // Used by Swift implementation
 pub fn is_admin_user(credentials: &Credentials) -> bool {
     credentials
         .claims