fix(pool): SimplePool.publish() should reject, not resolve, on connection failure

In publish(), the two early-exit failure cases (duplicate url,
allowConnectingToRelay returning false) correctly Promise.reject(). But the
ensureRelay() catch block instead returned a fulfilled string
("connection failure: " + err) — the one inconsistent case in the same
function.

This means Promise.any(pool.publish(...)) (the pattern this repo's own
README documents), or any other fulfilled-vs-rejected check, reports
success even when every relay connection failed, since Promise.any only
cares whether a promise settled as fulfilled, never what it resolved to.

Fix: reject with the same message instead of resolving with it, matching
the other two failure paths in this function. Added a test reproducing
the bug against an unreachable relay (confirmed failing before the fix,
passing after) using the existing mock-socket test infra — no new test
helpers needed, an unregistered mock URL already fails to connect the
same way a real unreachable relay would.

Verified: full suite passes except two pre-existing, unrelated failures
confirmed present on a clean checkout of master — nip77's live-network
test (unreachable from a sandboxed environment) and the timing-sensitive
ping-pong test.

abstract-pool.ts

@@ -407,7 +407,7 @@ export class AbstractSimplePool {
         })
       } catch (err) {
         this.onRelayConnectionFailure?.(url)
-        return String('connection failure: ' + String(err))
+        return Promise.reject('connection failure: ' + String(err))
       }
 
       return r

pool.test.ts

@@ -389,6 +389,32 @@ test('track relays when publishing', async () => {
   expect(pool.seenOn.get(event2.id)).toBeUndefined()
 })
 
+test('publish() rejects (does not resolve) when a relay is unreachable', async () => {
+  // ensureRelay()'s failure was previously swallowed and turned into a
+  // *resolved* string ("connection failure: ..."), so callers using the
+  // documented `Promise.any(pool.publish(...))` pattern (or any other
+  // fulfilled-vs-rejected check) would see success even when every relay
+  // was unreachable. It must reject like the pool's other early failure
+  // paths (duplicate url, allowConnectingToRelay) already do.
+  let event = finalizeEvent(
+    {
+      kind: 1,
+      created_at: Math.floor(Date.now() / 1000),
+      tags: [],
+      content: 'hello',
+    },
+    generateSecretKey(),
+  )
+
+  const unreachable = 'wss://nobody-is-listening.invalid.mock/nothing'
+  const [settled] = await Promise.allSettled(pool.publish([unreachable], event))
+
+  expect(settled.status).toBe('rejected')
+  if (settled.status === 'rejected') {
+    expect(String(settled.reason)).toContain('connection failure')
+  }
+})
+
 test('oninvalidevent is called through the pool for invalid events', async done => {
   const mockRelay = mockRelays[0]
   const relay = await pool.ensureRelay(mockRelay.url)