use --best for flac compression

[LuckyTurtleDev]

Currently whipper use the default flacc compression level. Flacc decompression speed is independent from its compression level (according to Wikipedia). Compression of 4h of wav files take my pc 3 seconds. The complete rip of a CD have always take more 15min.

So in total I do not see any reasons to not always apply the max compression level, since the time compressing is irrelevant in comparison to the cd read time.

[github-actions]

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