refactor(chain)!: Remove Anchor trait and make anchors unique to (Txid, BlockId)

[LagginTimes]

Resolves #1507.

Description

The Anchor trait has been removed and anchors are now unique to (Txid, BlockId).

Notes to the reviewers

Documentation have been mostly untouched and need to be written/updated.

Changelog notice

• Anchor trait has been removed.
• Anchor type and BlockTime struct have been added to bdk_chain.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

[notmandatory]

Overall looks like a nice simplification making Anchor a concrete type, and replacing ConfirmationBlockTime with BlockTime. I primarily focused on changes in tx_data_traits.rs as the rest of the changes are downstream.

Once docs are done this looks good to me.

@evanlinjin is it OK to merge this one before #1514 ?

[evanlinjin]

This is an initial look. Thanks for pushing so much work out in short notice.

[evanlinjin]

Suggested change

	txs: HashMap<Txid, (TxNodeInternal, BTreeMap<Anchor, AM>)>,
	txs: HashMap<Txid, (TxNodeInternal, BTreeSet<BlockId>)>,

Anchor contains the txid. It does not make as part of the value of something keyed by txid.

Also we can lookup the A (anchor meta) from anchors.

[evanlinjin]

Suggested change

	pub anchors: &'a BTreeMap<Anchor, AM>,
	pub anchors: Range<'a, Anchor, AM>,

I'm not sure if this will work? Getting a range from TxGraph::anchors.

[evanlinjin]

@notmandatory I prefer we rebase this on top of #1514 since that PR is more "final" than this one.

[evanlinjin]

As discussed privately, it makes sense to rm TxGraph::anchors field.

pub struct TxGraph<AM = BlockTime> {
    // all transactions that the graph is aware of in format: `(tx_node, tx_anchors)`
    txs: HashMap<Txid, (TxNodeInternal, BTreeMap<BlockId, AM>)>,
    spends: BTreeMap<OutPoint, HashSet<Txid>>,
    last_seen: HashMap<Txid, u64>,


    // This atrocity exists so that `TxGraph::outspends()` can return a reference.
    // FIXME: This can be removed once `HashSet::new` is a const fn.
    empty_outspends: HashSet<Txid>,
}

See P.O.C: 63d9e6a

[evanlinjin]

This is great work. However, we have concluded that we do not have enough time to get this into v1.0.beta (as discussed).

[notmandatory]

I'll move this out of the alpha milestone, thanks guys.

[notmandatory]

Technically wallet ChangeSet is part of the public wallet API I'll move this to 2.0.