cleanup: remove #[serial] annotations from e2e_test, scanner, lifecycle, and object-capacity crates

Remove no-op #[serial] attributes (nextest ignores serial_test) and the
serial_test dependency from four crates. All tests already use temp_env
for env-var isolation, making #[serial] purely redundant.

Crates cleaned:
- e2e_test (37 annotations, 9 imports, removed serial_test dep)
- rustfs-scanner (115 annotations across 7 files, removed serial_test dep)
- rustfs-lifecycle (46 annotations, removed serial_test dep)
- rustfs-object-capacity (38 annotations, removed serial_test dep)

Also converted scanner/tests/lifecycle_integration_test.rs
with_forced_immediate_enqueue_timeout helper from unsafe raw
env::set_var/remove_var to temp_env::async_with_vars for proper
isolation, and added async_closure feature to scanner's temp-env dep.

crates/e2e_test/src/get_stream_failure_observability_test.rs

@@ -51,7 +51,6 @@ mod tests {
     use aws_sdk_s3::Client;
     use aws_sdk_s3::primitives::ByteStream;
     use aws_sdk_s3::types::{CompletedMultipartUpload, CompletedPart};
-    use serial_test::serial;
     use std::error::Error;
     use tokio::time::{Duration, timeout};
     use tracing::info;
@@ -129,7 +128,6 @@ mod tests {
     /// the body — and assert the server log names the object, at the log level a
     /// default deployment actually runs with.
     #[tokio::test]
-    #[serial]
     async fn midstream_get_failure_is_logged_with_the_object_at_default_log_level() -> TestResult {
         init_logging();
         info!("rustfs#4784: a mid-stream GET failure must name its object in the source log");