The previous commit b9c5b9d08b040faf6c6b2d9b3745918031555b72 added
IndexSpk. This goes further and adds `Indexed` and `KeychainIndexed`
type alises (IndexSpk is Indexed<ScriptBuf>) and attempts to standardize
the structure of return types more generally.
The underlying SpkTxOutIndex should not use DescriptorIds to index
because this loses the ordering relationship of the spks so queries on
subranges of keychains work.
Along with that we enforce that there is a strict 1-to-1 relationship
between descriptors and keychains. Violating this leads to an error in
insert_descriptor now.
In general I try to make the translation layer between the SpkTxOutIndex
and the KeychainTxOutIndex thinner. Ergonomics of this will be improved
in next commit.
The test from the previous commit passes.
Previously there was a tx cache that you passed in as part of the sync
request. This seems bad and the example show'd that you should copy all
your transactions from the transaction graph into the sync request every
time you sync'd. If you forgot to do this then you would always download everything.
Instead just do a plain old simple cache inside the electrum client.
This way at least you only download transactions once. You can
pre-populate the cache with a method also and I did this in the examples.
