Merge bitcoindevkit/bdk#1612: Refactor: Move transaction testing utilities from ...

88a8403707038264251b3e7fa18b8f21af8646ff refactor(test): move tx test utils to testenv (Vihiga Tyonum)

Pull request description:

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  ### Description

  This change moves all transaction testing utilities (macros and functions) from `crates/chain/tests/common` to `crates/testenv/tx_utils` to minimize duplication.

  Closes #1602

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  ### Notes to the reviewers

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  ### 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
  * [ ] I've added docs for the new feature

  #### Bugfixes:

  * [ ] This pull request breaks the existing API
  * [ ] 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:
  ValuedMammal:
    ACK 88a8403707038264251b3e7fa18b8f21af8646ff
  notmandatory:
    ACK 88a8403707038264251b3e7fa18b8f21af8646ff

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