fix(transaction): copy AwaitingFeePayer in Tx.Clone()

[CrytoInsight]

fix(transaction): copy AwaitingFeePayer in Tx.Clone()

Summary

Tx.Clone() copied every field of the transaction except AwaitingFeePayer. For
sponsored (fee-payer) transactions this silently changes the bytes the sender signs,
so a signature produced over a clone never verifies on chain.

Root cause

SerializeForSigning branches on AwaitingFeePayer:

skipFeeToken := opts.ForSigning && opts.Format == FormatNormal &&
    (tx.AwaitingFeePayer || tx.FeePayerSignature != nil)

When the flag is true the signing payload (a) skips fee_token and (b) writes the
0x00 fee-payer marker in field 11. Clone() left the flag at its zero value
(false), so the clone serialized to the non-sponsored form instead.

Impact

• Severity: high
• A clone of a sponsored tx is signed over a different payload than the original.
• The sender signature fails verification once a fee payer sponsors it — funds path
  for sponsored transactions is broken, and the failure is silent until broadcast.
• Clone() is explicitly documented for producing transaction variations, so this is
  on the happy path.

Fix

Add the missing field to the struct literal in Clone():

AwaitingFeePayer: tx.AwaitingFeePayer,

Verification

TestClonePreservesAwaitingFeePayer asserts the original and the clone produce an
identical signing hash. Fails before the change, passes after. go test ./pkg/transaction/
is green.

[brendanjryan]

Thanks for the PR! Rolled fwd with your commits in the linked PR