test(ecstore): deflake multipart listing tests under plain cargo test (#5730)

Multipart upload ids embed the process-global deployment id at both create time and list time. Under plain cargo test (thread-parallel, shared process globals) a concurrently running test that re-initializes a store can swap the global between the two reads, making full-upload-id equality assertions fail spuriously (observed: core::sets::tests::list_multipart_uploads_merges_all_sets_without_pagination_loss failing when run concurrently with bucket::quota tests, passing in isolation).

Add a test-only upload_uuid_suffix helper next to deployment_upload_id and make the affected assertions compare only the decoded <uuid>x<timestamp> suffix. Where suffix normalization changes within-key ordering (base64 alphabet order is not byte order), both sides are sorted before comparison. nextest/CI is unaffected (process-per-test); this only hardens local plain cargo test runs.

crates/ecstore/src/runtime/sources.rs

@@ -246,6 +246,22 @@ pub fn deployment_id() -> Option<String> {
     get_global_deployment_id()
 }
 
+/// Test-only inverse of [`deployment_upload_id`]: returns the raw
+/// `<uuid>x<timestamp>` suffix without the deployment-id prefix. Under plain
+/// `cargo test` (thread-parallel, shared process globals) a concurrently
+/// running test that re-initializes a store can swap the global deployment id
+/// between create time and list time, so assertions must compare only this
+/// suffix, never the full encoded upload id.
+#[cfg(test)]
+pub(crate) fn upload_uuid_suffix(upload_id: &str) -> String {
+    base64_simd::URL_SAFE_NO_PAD
+        .decode_to_vec(upload_id.as_bytes())
+        .ok()
+        .and_then(|decoded| String::from_utf8(decoded).ok())
+        .and_then(|decoded| decoded.split_once('.').map(|(_, suffix)| suffix.to_owned()))
+        .unwrap_or_else(|| upload_id.to_owned())
+}
+
 pub(crate) fn replication_pool() -> Option<Arc<DynReplicationPool>> {
     crate::runtime::global::current_ctx().replication_pool()
 }