cd8d3bd937 wallet: use outpoint when estimating input size (Lőrinc)
Pull request description:
### Problem
`CalculateMaximumSignedInputSize()` is passed the outpoint being sized, but a previous refactor stopped using that context when estimating the signed input size.
This could make externally selected inputs look slightly smaller than they really are.
### Fix
Pass the outpoint through again when estimating the signed input size.
Add a regression test for the external-input case.
> [!NOTE]
> the branch name still reflects the previous state of this PR, where the unused parameter was removed instead of wired back in
ACKs for top commit:
achow101:
ACK cd8d3bd937
pablomartin4btc:
ACK cd8d3bd937
Tree-SHA512: 6089ae65ae12677c32be0556d704f8c179f1ff5a017690846ae495644890526f85d8c0d75d4ec4c3c9ac5b519251169009484623340b8bc3a87fa9a3be27fefd
b796bf44f3