Merge bitcoindevkit/bdk#2031: Add `verify-standalone` and `verify-standalone-all...

eeb69dced18785408b735c64522430a2104b885e chore(just): Add `verify-standalone-all` recipe (志宇)
37411ea4713a8706c3af9beda24494f99649fed7 chore(just): Add `verify-standalone` recipe (志宇)

Pull request description:

  Fixes #2030

  ### Description

  Adds two `just` recipes that check whether workspace crates build as they would once published:

  * `verify-standalone <crate> [args]` (alias `vs`): packages the crate and builds the packaged copy outside the workspace, so sibling workspace crates resolve from crates.io instead of local paths. A failure usually means the crate uses something from a sibling crate that isn't released yet. Extra args are passed to `cargo build`.
  * `verify-standalone-all [args]` (alias `vsa`): runs `verify-standalone --all-features` on every publishable workspace crate, stopping at the first failure. `--all-features` catches uses of unreleased APIs behind non-default features.

  The registry cache and build artifacts are kept under the target directory, so repeat runs are fast.

  ### Notes to the reviewers

  Neither recipe is wired into CI. On current `master`, `bdk_chain` and `bdk_bitcoind_rpc` fail because they use `bdk_core` APIs that aren't released yet, which is what the check is for.

  ### Checklists

  #### All Submissions:

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

  🤖 Generated with [Claude Code](https://claude.com/claude-code)

ACKs for top commit:
  evanlinjin:
    self-ACK eeb69dced18785408b735c64522430a2104b885e

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