Use move in WeakRingBuffer where capable. Allow one-sized ring buffers

[Hattonuri]

By this time we are not allowed to create one-sized channel just because of asserts

i suppose this is because of: https://github.com/khizmax/libcds/blob/9985d2a87feaa3e92532e28f4ab762a82855a49c/cds/opt/buffer.h#L343

but 1 & (0) == 0 . so its a valid power of two

[TomlyYang]

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