Merge bitcoindevkit/bdk#2233: test(core): cover SyncRequest inspect progress and...

6c363335cf0462afdb8b467fd5385139cd30d1fa test(core): cover SyncRequest inspect progress and expected txid merging (haoshengzhen)

Pull request description:

  ### Description

  Adds unit tests for `SyncRequest` in `bdk_core::spk_client`:
  - the `inspect` callback sees progress *after* each spk/txid/outpoint is consumed.
  - `expected_spk_txids` merges txids across calls for the same spk, and other spks get none.

  ### Changelog notice

  None, test-only.

ACKs for top commit:
  evanlinjin:
    ACK 6c363335cf0462afdb8b467fd5385139cd30d1fa

Tree-SHA512: 532754e960ea14a665f1d59e2349bf0ecd270d1beb4ded8636d0c569bff0e60c3224ba28263b5187689c993e34180d9585cc6abe2024209ce2c20faf443124dd