Merge bitcoindevkit/bdk#1738: test(core): add unit tests for `merge` trait

fcc0a3409aa390e9f32a3308dd5fe0e2e33b9b44 test: add tests for  trait of operations on various data structures, including conflict scenarios and checking for empty structures (pluveto)

Pull request description:

  ### Description

  This update adds unit tests for the `Merge` trait implementations on `BTreeMap`, `BTreeSet`, `Vec`, and tuples. It also includes tests for the `is_empty` and `take` methods to ensure their correct functionality.

  ### Notes to the Reviewers

  - The tests cover basic scenarios for merging collections and checking their emptiness.
  - Consider the potential method name conflict with `BTreeSet`'s existing `take` method.

  ### Changelog Notice

  - Added unit tests for merging functionality and utility methods (`is_empty`, `take`) on various collection types.

  ### 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.

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Tree-SHA512: fdcd67ca9127986e9ce9aa9ccc3276aaff127fa9333696c61ff2ca1b37a2ce8f9fe7af8e06ab57dda493741e91fa63a3aba58a1338a17090626225899e6c7588