fix(create_tx,bump_fee): return errors instead of panicking

fix(create_tx,bump_fee): return errors instead of panicking

`create_tx` and `bump_fee` called `.unwrap()` on `Result`s carrying
user-supplied input, so a mistyped argument aborted the process with a
Rust panic (exit 101) instead of a usage error (exit 1).

- propagate `add_utxos` failures in `create_tx` and `bump_fee` with `?`,
  adding `BDKCliError::AddUtxoError` so the malformed outpoint is named
- propagate `--add_data` base64 decoding and `PushBytesBuf` conversion
  failures in `create_tx`
- stop flattening `add_utxos` errors into `CreateTxError::UnknownUtxo`
in `create_sp_tx` and `create_dns_tx`, which discarded the real cause
- add an integration test asserting exit 1, never 101, for an unknown
  outpoint and for malformed base64

Fixes #325