fix: Add missing fields to Transaction.CopyTo and PoolPolicy.Return

[Fallengirl]

CopyTo was missing IsAnchorTx field - this breaks gas estimation for Taiko anchor transactions since TaikoTransactionProcessor checks this flag for special handling (skip validation, no gas purchase, no refunds).

PoolPolicy.Return wasn't resetting:

• IsAnchorTx (Taiko)
• SourceHash, Mint, IsOPSystemTransaction (Optimism deposit tx fields)
• _spentGas

These fields persist between pooled object reuses, causing data leakage. A normal tx could inherit IsAnchorTx=true or Optimism deposit data from previously returned transaction.