Bad name in ReadableSize

[jiacai2050]

Describe this problem

https://github.com/CeresDB/ceresdb/blob/659b55985a14f835cff5bbb2df4eea1b0a540366/common_util/src/config.rs#L149

In ReadableSize, there is a method called as_bytes(), which is very confusing, since the original meaning of as_bytes is to return &[u8], not u64

Steps to reproduce

No required.

Expected behavior

No response

Additional Information

I suggest we name it as_byte to follow other methods in ReadableSize