Chunk home filters to avoid hitting max filter item limits

When a user is following several accounts, they may get a stale feed
caused by the subscription request being rejected by relays (due to max filter item limits).

This commit implements a fix that gets around the issue by
creating several chunked filters for the home feed event and contact
metadata subscriptions.

This is a short to medium-term practical fix, where we get around the
practical limitations imposed by most relays. In the future we should
work on longer-term solutions, which will likely require protocol improvements

Main Test
---------

Procedure:
1. Login with Elsat's npub (Or some account that follows about 2K people)
2. Check the home feed. There should be fresh notes.

REPRO:
Device: iPhone 15 simulator
iOS: 17.4
Damus: 1.9 (3) (0d9954290a)
Results:
- No fresh notes, most recent post is from several hours ago (Feed is stale)

FIX TEST:
Device: iPhone 15 simulator
iOS: 17.4
Damus: This commit
Results:
- Fresh notes appear, most recent post is from a few seconds ago.

Other testing:
--------------

- New automated test passing
- All other automated tests passing
- Tested scrolling down the feed on these conditions:
  - Device: iPhone 13 Mini
  - iOS: 17.4.1
  - Accounts:
    - One with about 160 contacts and 10 relays (Daniel D’Aquino)
    - One with about 1K+ contacts and 9 relays (Freedom Smuggler)
    - One with about 981 contacts and 6 relays (jb55)
    - Elsat's account (2K+ accounts and 8 relays)
  - Result: None of those were stale

Changelog-Fixed: Fix stale feed issue when follow list is too big
Closes: https://github.com/damus-io/damus/issues/2194
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
Reviewed-by: William Casarin <jb55@jb55.com>

damus/Util/Extensions/Array.swift

@@ -0,0 +1,26 @@
+//
+//  Array.swift
+//  damus
+//
+//  Created by Daniel D’Aquino on 2024-05-10.
+//
+
+import Foundation
+
+extension Array {
+    /// Splits the array into chunks of the specified size.
+    /// - Parameter size: The maximum size of each chunk.
+    /// - Returns: An array of arrays, where each contained array is a chunk of the original array with up to `size` elements.
+    func chunked(into size: Int) -> [[Element]] {
+        guard size > 0 else { return [self] }
+        return stride(from: 0, to: count, by: size).map {
+            Array(self[$0..<Swift.min($0 + size, count)])
+        }
+    }
+}
+
+extension Array where Element: Equatable {
+    mutating func removeAll(equalTo item: Element) {
+        self.removeAll(where: { $0 == item })
+    }
+}