Merge bitcoindevkit/bdk#2013: ci: pin `rayon` dependencies for msrv

Merge bitcoindevkit/bdk#2013: ci: pin `rayon` dependencies for msrv

763b29e1d27049d52b742c2fcff9180b46863105 ci: pin `rayon` dependencies for msrv (Wei Chen)

Pull request description:

  ### Description

  Pinned `rayon = 1.10.0` and `rayon-core = 1.12.1` for 1.63 and 1.75 MSRV.

  ### Changelog notice

  - Pin `rayon 1.10.0` and `rayon-core 1.12.1` for MSRV.

  ### Checklists

  #### All Submissions:

  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)

ACKs for top commit:
  ValuedMammal:
    utACK 763b29e1d27049d52b742c2fcff9180b46863105
  evanlinjin:
    ACK 763b29e1d27049d52b742c2fcff9180b46863105

Tree-SHA512: 2de7ebad9889e1ff89d13051d872ea72acb8c684c5397833c263643dcdb440d24727f2477d705450ea2b034dc371f9f925004f90745de5f52b58371479b9be39