8305e648494cbdd1f6438904ec367f8442fba606 feat(chain): expose `SpkIterator::new_with_range` (志宇)
Pull request description:
### Description
This method is useful, I'm not sure why it is not public.
I've also updated the docs and tests.
### Changelog notice
Added
* Expose `SpkIterator::new_with_range`
### 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:
* [x] I've added tests for the new feature
* [x] I've added docs for the new feature
ACKs for top commit:
danielabrozzoni:
utACK 8305e648494cbdd1f6438904ec367f8442fba606
LLFourn:
ACK 8305e648494cbdd1f6438904ec367f8442fba606
Tree-SHA512: 26389bf65bea74742ebb4d170f3d21aeb02e5be1b3fd20ef16eb318393145809d2b21b96767ebb42acfd8dd789a82bb2d7b29ded24249dabf06bd1e6d23cf0cf