Instead of relying on a `OwnedIndexer` trait to filter for relevant
txouts, we move the listing and balance methods from `IndexedTxGraph` to
`TxGraph` and add an additional input (list of relevant outpoints) to
these methods.
This provides a simpler implementation and a more flexible API.
* Introduce `LocalChain::inner` method to get the inner map of block
height to hash.
* Replace `LocalChain::get_block` (which outputted `BlockId`, thus able
to return invalid representation) with `get_blockhash` that just
returns a `BlockHash`.
* Remove `TODO` comments that should be github tickets.
If `BlockId` implements `Anchor`, the meaning is ambiguous. We cannot
tell whether it means the tx is anchors at the block, or whether it also
means the tx is confirmed at that block.
Instead, `ConfirmationHeightAnchor` and `ConfirmationTimeAnchor` structs
are introduced as non-ambiguous `Anchor` implementations.
Additionally, `TxGraph::relevant_heights` is removed because it is also
ambiguous. What heights are deemed relevant? A simpler and more flexible
method `TxGraph::all_anchors` is introduced instead.
Instead of forcing all transactions inserted to use the same anchors, we
change the API to have unique anchors per transaction.
This allows for more flexibility in general. For example, use `Anchor`
implementations that contain the position in a block of a transaction.
The `insert_relevant_txs` test has also been changed to used
`KeychainTxOutIndex` so that index additions can be checked
(`SpkTxOutIndex` has no additions).
Additionally, generic bounds of some `IndexedTxGraph` list methods have
been fixed.
