feat: add support for broadcast replay configuration

[grdsdev]

Summary

• Added ReplayOption struct for configuring broadcast replay
• Added replay field to BroadcastJoinConfig
• Added public initializer to BroadcastJoinConfig to support replay configuration

Changes

This PR implements broadcast replay support following the pattern from realtime-js PR #540:

1. ReplayOption: New struct with since (Int) and optional limit (Int?)
2. BroadcastJoinConfig: Added optional replay field
3. Public initializer: Added to enable replay configuration

Usage

// Configure broadcast with replay
let config = RealtimeJoinConfig(
  broadcast: BroadcastJoinConfig(
    acknowledgeBroadcasts: true,
    receiveOwnBroadcasts: true,
    replay: ReplayOption(
      since: 1234567890,
      limit: 100
    )
  )
)

let channel = supabase.realtimeV2.channel("my-channel", config: config)

// Broadcast callback receives meta field
channel.onBroadcast { message in
  if let meta = message.payload["meta"] as? [String: Any],
     let replayed = meta["replayed"] as? Bool,
     replayed {
    print("Replayed message: \(meta["id"] ?? "")")
  }
}

await channel.subscribe()

Test plan

• Verify type checking passes
• Test broadcast replay configuration
• Verify meta field is properly included in callbacks

🤖 Generated with Claude Code

[coveralls]

Pull Request Test Coverage Report for Build 18141289223

Details

• 5 of 9 (55.56%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 77.778%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
Sources/Realtime/RealtimeJoinConfig.swift	5	9	55.56%

Totals
Change from base Build 18098073005:	-0.03%
Covered Lines:	5593
Relevant Lines:	7191

---

💛 - Coveralls