Add a Swift version of WalletSetupBip32

[RowDaBoat]

Description

Showing users how the APIs can be used across languages is valuable. This PR mirrors the WalletSetupBip32 JVM example in Swift as requested in issue 818.

Notes to the reviewers

This Swift example follows the Kotlin example as closely as possible.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran swift build and swift run before committing
• I've linked the relevant upstream docs or specs above

New Features:

• I've added the new feature to the CI build
• I've added docs for the new feature

[j-kon]

Thanks for adding this Swift example. I found one user-facing issue that should be fixed before this lands.

bdk-swift/README.md documents swift run WalletSetupBip32Example, but the executable added in bdk-swift/Package.swift is named WalletSetupBip32, and the CI change builds that same target. As written, the README command will fail because there is no executable product with that name.

I think the README command should be changed to swift run WalletSetupBip32.

Aside from that, this looks aligned with issue #818 and mirrors the JVM example closely.

[j-kon]

ACK