MINOR: add inserted_at column to trades

[ycdesu]

A trade may be missed initially and fetched after it has occurred, so we add inserted_at column.

[CLAassistant]

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[c9s]

好像還是 test fail 可能要 rebase 一下 我猜可能是 bitget test failed

[c9s]

@ycdesu you need to sign CLA~ thanks