fix(query-core): use explicit undefined check for timer IDs

  Custom TimeoutProvider implementations may return 0 as a valid timer
  ID (e.g. a counter-based provider), but the existing truthy checks
  treated 0 as "no timer" and skipped clearTimeout/clearInterval. This
  left stale timers running, causing unexpected refetches and GC leaks.

  Compare against undefined instead, matching the optional `?:
  ManagedTimerId` field types.

  Fixes #10395

Author: semimikoh

packages/query-core/src/queryObserver.ts

@@ -417,14 +417,14 @@ export class QueryObserver<
   }
 
   #clearStaleTimeout(): void {
-    if (this.#staleTimeoutId) {
+    if (this.#staleTimeoutId !== undefined) {
       timeoutManager.clearTimeout(this.#staleTimeoutId)
       this.#staleTimeoutId = undefined
     }
   }
 
   #clearRefetchInterval(): void {
-    if (this.#refetchIntervalId) {
+    if (this.#refetchIntervalId !== undefined) {
       timeoutManager.clearInterval(this.#refetchIntervalId)
       this.#refetchIntervalId = undefined
     }

packages/query-core/src/removable.ts

@@ -30,7 +30,7 @@ export abstract class Removable {
   }
 
   protected clearGcTimeout() {
-    if (this.#gcTimeout) {
+    if (this.#gcTimeout !== undefined) {
       timeoutManager.clearTimeout(this.#gcTimeout)
       this.#gcTimeout = undefined
     }