gui: brand new volume slider

[cosven]

The older volume slider has two problems

1. UX is not good
2. drag the slider causes the app hang. Worse,

   正在播放时拖动音量导致界面卡死，xorg 下几乎卡死整个 xserver，wayland 下留一个音量条始终在顶部，主界面被 kwin 标记为灰色，音乐正常播放
   此时 htop 看到所有进程均分 100% CPU（大概是得谢谢 GIL），命令行 fuo status 会卡死
   本次 Syu 的 log https://fars.ee/Ginq 包含 upgraded feeluown (4.0.1-1 -> 4.1-1)

Now, introducing a self-painting slider to solve these problems.
User can use up/down or mouse to adjust the volume.

[coveralls]

Pull Request Test Coverage Report for Build 8120910363

Details

• 25 of 53 (47.17%) changed or added relevant lines in 2 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.07%) to 55.237%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
feeluown/gui/drawers.py	1	2	50.0%
feeluown/gui/widgets/volume_button.py	24	51	47.06%

Files with Coverage Reduction	New Missed Lines	%
feeluown/gui/widgets/selfpaint_btn.py	2	49.43%
feeluown/library/library.py	3	71.49%

Totals
Change from base Build 8030202694:	-0.07%
Covered Lines:	9055
Relevant Lines:	16393

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💛 - Coveralls