feature: add block_headers and blocks streams full APIs (w/ checkpoint and reorg handling)

.github/pull_request_template.md

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+<!-- You can erase any parts of this template not applicable to your Pull Request. -->
+
+### Description
+
+<!-- Describe the purpose of this PR, what's being adding and/or fixed -->
+
+### Notes to the reviewers
+
+<!-- In this section you can include notes directed to the reviewers, like explaining why some parts
+of the PR were done in a specific way -->
+
+### Checklists
+
+#### All Submissions:
+
+* [ ] I've signed all my commits
+* [ ] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
+* [ ] I ran `cargo fmt` and `cargo clippy` before committing
+
+#### New Features:
+
+* [ ] I've added tests for the new feature
+* [ ] I've added docs for the new feature
+* [ ] I've updated `CHANGELOG.md`
+
+#### Bugfixes:
+
+* [ ] This pull request breaks the existing API
+* [ ] I've added tests to reproduce the issue which are now passing
+* [ ] I'm linking the issue being fixed by this PR

CHANGELOG.md

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+# Changelog
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+- Add `block_events::websocket` client, and a `websocket::listen_new_block_headers` fn to get a stream of websocket messages.
+- Add `block_events::http` client, and multiple fns to consume data from mempool.space and/or esplora REST APIs.
+- Add `block_events::api` with multiple structs and definition for responses, such as: `BlockExtended` and events as `BlockEvent`
+- Add `block_events::subscribe_to_block_headers` fn in order to return a `Stream` of `block_events::api::BlockEvent(bitcoin::BlockHeader)`.
+- Add `block_events::process_blocks` to handle block reorganization, manage in-memory cache struct `BlockHeadersCache`, and propagate errors to caller.
+- Add `block_events::subscribe_to_blocks` fn in order to return a `Stream` of `block_events::api::BlockEvent(bitcoin::Block)`.