Fix background database account refresh stopping in multi-writer accounts

In multi-writer accounts, refreshLocationPrivateAsync() stops the background
refresh timer when shouldRefreshEndpoints() returns false. This means topology
changes (e.g., multi-write to single-write transitions) go undetected until
the next explicit refresh trigger.

The .NET SDK (azure-cosmos-dotnet-v3) correctly continues the background
refresh loop unconditionally - the loop only stops when canRefreshInBackground
is explicitly false, not when shouldRefreshEndpoints returns false.

This fix adds startRefreshLocationTimerAsync() to the else-branch of
refreshLocationPrivateAsync(), ensuring the background timer always reschedules
itself regardless of whether endpoints currently need refreshing.

Without this fix, after a multi-write -> single-write -> multi-write transition,
reads remain stuck on the primary region because the SDK never re-reads account
metadata to learn about the restored multi-write topology.

Related: PR #6139 (point #4 in description acknowledged this bug)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jeet1995

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/GlobalEndpointManager.java

@@ -245,6 +245,16 @@ private Mono<Void> refreshLocationPrivateAsync(DatabaseAccount databaseAccount)
                 return Mono.empty();
             } else {
                 logger.debug("shouldRefreshEndpoints: false, nothing to do.");
+
+                // Even when no endpoint refresh is needed right now, we must keep the
+                // background refresh timer running so that future topology changes
+                // (e.g., multi-write <-> single-write transitions) are detected.
+                // This aligns with the .NET SDK behavior where the background loop
+                // continues unconditionally as long as the client is alive.
+                if (!this.refreshInBackground.get()) {
+                    this.startRefreshLocationTimerAsync();
+                }
+
                 this.isRefreshing.set(false);
                 return Mono.empty();
             }