[React] Implement multi-participant handling & state

[Regaddi]

This PR implements handling for multi-participant sessions. The local participant and bot are still referenced via "local" and "bot". Remote participants are returned through the usePipecatClientParticipantIds hook (can include "local" and "bot", too). We keep track of the bot's participant id to correctly distinguish between bot and remote participant tracks.

I have already outlined the changes in the changelog:

Added

• Multi-participant support: Full support for handling multiple participants in sessions
  • New usePipecatClientParticipant() hook to access individual participant data
  • New usePipecatClientParticipantIds() hook to get all participant IDs with filtering options
  • Support for both regular and screen share media tracks per participant

Changed

• PipecatClientVideo component now requires participantId prop when participant is set to "remote"
• Enhanced PipecatClientAudio component now renders audio for all participants automatically
• Enhanced PipecatClientVideo component now supports remote participants
• usePipecatClientMediaTrack() hook signature updated to support remote participants