Merge bitcoindevkit/bdk#2148: `chain 0.23.x`: Fix panic in scan loop and update msrv...

Merge bitcoindevkit/bdk#2148: `chain 0.23.x`: Fix panic in scan loop and update msrv and esplora-client

2ee48d7b5199d9a4ef8626b2ff87e124f8897604 fix(esplora): Bump `esplora-client` to `0.12.3` (志宇)
af6791f3db090809e2919bc73ab362df7a675c3e ci: Fix `ci/pin-msrv.sh` (志宇)
fb3e169e72ea2246ac98ed1b2bf6fec3de663ac4 ci: Fix pin msrv for 1.75.0 (志宇)
8d2ca9b7750d324a2d1fae5d01326f0ff1d4ea48 fix: remove panic from stop gap scan loop (Matthew)

Pull request description:

  ### Description

  Backport of #2053, #2136. Also fixes CI MSRV issues.

  Replaces #2147 - Purely MSRV fixes still resulted in CI failure due to clippy.
  Replaces #2141 - Might as well include the whole PR backport.

  ### Changelog notice

  ```md
  Fixed:
  - Avoid a panic in the Esplora stop‑gap scan loop by tracking consecutive unused scripts to compute the gap boundary.
  - Bump `esplora_client` to `0.12.3` so that the `.get_block_infos` method is always available.
  ```

  ### Checklists

  #### All Submissions:

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

ACKs for top commit:
  luisschwab:
    ACK 2ee48d7b5199d9a4ef8626b2ff87e124f8897604
  oleonardolima:
    ACK 2ee48d7b5199d9a4ef8626b2ff87e124f8897604

Tree-SHA512: 0f183e2b5ffc6629298f960f22e95020df58da98171c69e880afab5d57f337af240ff7ad97244f3f052d3b1a3fdd8a91543b5a943eeac2234de02672fc94d3f2