fix: correctly treat confirmation for watch_pending_transaction

[klkvr]

Motivation

Current logic was not treating confirmations in the expected way (tx being included = 1 confirmation)
Also split_off splits off keys including the one at which split is being performed, thus we actually notified TxWatcher about txses one block later

Two open questions:

1. Currently if tx is sent, included into block and one more block is mined (basically tx included into block X and latest block is X+1), then call to watch_pending_transaction will indefinitely wait for a block with targeted tx. Is this expected? Feels like a footgun, especially considering that we don't have a default timeout
2. It feels like watch_pending_transaction users specifying confirmations > 1 would also be interested in ensuring that no reorg has happened and that tx is actually on-chain, should we add a parameter for that?

[prestwich]

please put open questions in issues 👍

[mattsse]

I believe this is correct