volume-pipewire: add flat-list sink+port cycling on click

[brkay54]

Summary

• Replace sink-only cycling with a flat-list approach that enumerates all (sink, port) pairs across every available sink
• Left/right click now cycles through every distinct output (e.g. Bluetooth → Speaker → Headphones) instead of being stuck when multiple ports exist on a single sink
• Active port label is appended to the display name when a sink has more than one port (e.g. ALC257 Analog/Headphones)

Problem

When a system has a single sink with multiple ports (e.g. built-in audio with Speaker and Headphones), the previous set_default_playback_device_next function found only one sink and did nothing on click.

Solution

Added two functions:

• get_all_outputs — enumerates all sink|port pairs via pactl list sinks
• set_next_audio_output — finds the current (sink, port) in the flat list, advances by ±1, then calls pactl set-default-sink and/or pactl set-sink-port as needed

Test plan

• Left-click cycles forward through all outputs
• Right-click cycles backward
• Audio streams follow to the new output
• Block label updates to reflect active port when sink has multiple ports
• Works with Bluetooth sink connected alongside internal audio

[brkay54]

@vivien need just a quick look, i have tested on my device it works.