Adapt delayed leave timings when delegation is available

Splits the config options for the timings of a delayed leave event into two sets: one for when delegation is available (as you can relax the timings and get more stable calls this way), and another for when it's unavailable (as we must continue to gracefully downgrade even after Matrix 2.0 is fully rolled out).

This works by bluntly hitting the delegation endpoints without auth before joining to check for a 404.

src/utils/observable.test.ts

@@ -9,9 +9,30 @@ import { expect, test } from "vitest";
 import { type Observable, of, Subject, switchMap } from "rxjs";
 
 import { withTestScheduler } from "./test";
-import { filterBehavior, generateItems, pauseWhen } from "./observable";
+import { or$, filterBehavior, generateItems, pauseWhen } from "./observable";
 import { type Behavior } from "../state/Behavior";
 
+const yesNo = {
+  y: true,
+  n: false,
+};
+
+test("or$", () => {
+  withTestScheduler(({ behavior, expectObservable }) => {
+    const input1Marbles = "ny--n--";
+    const input2Marbles = "n-y--n-";
+    const input3Marbles = "n--y--n";
+    const outputMarbles = "nyyyyyn";
+    expectObservable(
+      or$(
+        behavior(input1Marbles, yesNo),
+        behavior(input2Marbles, yesNo),
+        behavior(input3Marbles, yesNo),
+      ),
+    ).toBe(outputMarbles, yesNo);
+  });
+});
+
 test("pauseWhen", () => {
   withTestScheduler(({ behavior, expectObservable }) => {
     const inputMarbles = " abcdefgh-i-jk-";