8ab58af093ff295b86c3f8189aa96dea313092c4 feat(chain)!: wrap `TxGraph` txs with `Arc` (志宇)
Pull request description:
### Description
This PR makes `TxGraph` store transactions as `Arc<Transaction>`.
`Arc<Transaction>` can be shared between the chain-source and receiving structures. This allows the chain-source to keep the already-fetched transactions (save bandwith) and have a shared pointer to the transaction (save memory).
Our current logic to avoid re-fetching transactions is to refer back to the receiving structures. However, this means an additional round of locking our receiving structures.
### Notes to the reviewers
This will make more sense once I update the esplora/electrum chain sources to make use of both #1369 and this PR. The result would be chain sources which would only require locking the receiving structures twice (once for initiating the update, and once for applying the update).
### Changelog notice
* Changed `TxGraph` to store transactions as `Arc<Transaction>`. This allows chain-sources to cheaply keep a copy of already-fetched transactions.
### Checklists
#### All Submissions:
* [x] I've signed all my commits
* [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
* [x] I ran `cargo fmt` and `cargo clippy` before committing
#### New Features:
* [ ] I've added tests for the new feature
* [x] I've added docs for the new feature
ACKs for top commit:
LLFourn:
ACK 8ab58af093ff295b86c3f8189aa96dea313092c4
notmandatory:
ACK 8ab58af093ff295b86c3f8189aa96dea313092c4
Tree-SHA512: 81d7ad35fed7f253a3b902f09a41aaef2877f6201d4f6e78318741bf00e4b898a8000d878ffcbfe75701094ce3e9021bd718b190a655331a9e11f0ad66bdb02f
19304c13ec