feat(miner): use []*ethapi.RPCTransaction in RPC response body

[davidtaikocha]

As suggested by Maciej:

One more concern: wouldn't it be more universal to return RPCTransaction in the taikoAuth_txPoolContentWithMinTip instead Transaction? The difference is that RCPTransaction include directly from field. I noticed that while parsing json using Rust Alloy library, which expects this field to be present by default (It can be parsed though with some simple workarounds, recovering from from signature).