BlockAnchor
* Introduce `GraphedTx` struct to access transaction data of graphed transactions. * Ability to insert/access anchors and "seen at" values for graphed transactions. * `Additions` now records changes to anchors and last_seen_at.
- rewrite some parts of the code to deal with older borrow checker - downgraded hashbrown
Disabled warnings for nursery/tmp_plan as it's going to be replaced anyways
This completes the move of things from https://github.com/LLFourn/bdk_core_staging
