991cb77b6fbeedbf52d1bd9aa6b3d680f8269969 fix(chain): filter coinbase tx not in best chain (Wei Chen)
Pull request description:
### Description
Fixes#1144.
Coinbase transactions cannot exist in the mempool and be unconfirmed. `TxGraph::try_get_chain_position` should always return `None` for coinbase transactions not anchored in best chain.
### 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
#### Bugfixes:
* [ ] This pull request breaks the existing API
* [x] I've added tests to reproduce the issue which are now passing
* [x] I'm linking the issue being fixed by this PR
ACKs for top commit:
notmandatory:
ACK 991cb77b6fbeedbf52d1bd9aa6b3d680f8269969
danielabrozzoni:
ACK 991cb77b6fbeedbf52d1bd9aa6b3d680f8269969
Tree-SHA512: 9e06d8404708eee050c96807a876a470303f4983666c82c56c17d97c2d4b72784e75271279fd393c53a6a967a352aea1ef2762da71ac4bb58f7a0c2f05354948
f382fa9230