docs(svelte-query): add JSDoc to the exported classes, methods, and arrow functions

packages/svelte-query/src/containers.svelte.ts

@@ -8,6 +8,10 @@ type Subscriber = (update: VoidFn) => void | VoidFn
  */
 export type Box<T> = { current: T }
 
+/**
+ * A {@link Box} whose `current` value is computed on each read, and that notifies the reactive
+ * contexts reading it through the given subscriber.
+ */
 export class ReactiveValue<T> implements Box<T> {
   #fn
   #subscribe
@@ -17,6 +21,10 @@ export class ReactiveValue<T> implements Box<T> {
     this.#subscribe = createSubscriber((update) => onSubscribe(update))
   }
 
+  /**
+   * Subscribes the reactive context reading it, then computes the value.
+   * @returns The value returned by the compute function.
+   */
   get current() {
     this.#subscribe()
     return this.#fn()

packages/svelte-query/src/utils.svelte.ts

@@ -19,6 +19,14 @@ function runEffect(
   }
 }
 type Getter<T> = () => T
+/**
+ * Runs `effect` whenever the reactive state read by `sources` changes, even if they return the
+ * same values, skipping the first run. The effect receives the new and previous values, and is
+ * called untracked, so only `sources` are tracked.
+ * @param sources - The getter, or array of getters, to watch.
+ * @param flush - Whether to run after (`'post'`) or before (`'pre'`) the DOM updates.
+ * @param effect - Called with the new and previous values. It may return a cleanup function.
+ */
 export const watchChanges = <T>(
   sources: Getter<T> | Array<Getter<T>>,
   flush: 'post' | 'pre',