Feat: Add bip329 wallet labels

[Musab1258]

Description

This PR adds BIP-329 wallet label support to bdk-cli, to fix #184. It uses the [bip329] crate to manage label data, persists it in a separate labels.jsonl file within the wallet's data directory (e.g. ~/.bdk-bitcoin/<wallet_name>/labels.jsonl), and keeps it decoupled from the wallet's SQLite/redb database. It also exports and imports label files.

This PR includes the following functionality:

• Set labels: It uses a new label offline subcommand to attach a human-readable label to either a transaction ID, address, or UTXO (outpoint).
• Persist labels: It ensures that Labels are loaded from disk at the start of every offline wallet command and saved back after the command completes, so they survive across sessions.
• Display labels: The unspent and transactions commands now include a Label column in both --pretty table output and standard JSON output, showing the stored label or an em dash if none exists.
• Import labels: The import_labels subcommand merges labels from an external BIP-329 JSONL file into the wallet's current label state. If a label for the same item already exists, it is overwritten by the imported one.
• Export labels: The export_labels subcommand writes the wallet's current label state to a user-specified BIP-329 JSONL file, suitable for backup or use in other BIP-329 compliant wallets.

Notes to the reviewers

• Labels are stored in a separate labels.jsonl file rather than inside the wallet database. This keeps the label format portable and interoperable with other BIP-329 compliant wallets.
• The Label import from bip329 is aliased as BipLabel in handlers.rs to avoid a name clash with the OfflineWalletSubCommand::Label variant brought into scope via use crate::commands::OfflineWalletSubCommand::*.
• The import_labels command uses the existing add_or_update_label helper to merge incoming labels one at a time, new label references are inserted, and existing label references are overwritten by the imported value.
• The export_labels command writes to a user-specified path, which is independent of the wallet's internal labels.jsonl file. The internal file is always managed automatically by the save-on-exit mechanism, so the two files remain separate.

Changelog notice

Added

• New label subcommand to OfflineWalletSubCommand for tagging transactions, addresses, and UTXOs with human-readable labels.
• New import_labels subcommand to merge labels from an external BIP-329 JSONL file into the wallet's current label state.
• New export_labels subcommand to back up the wallet's current label state to a user-specified BIP-329 JSONL file.
• BIP-329 compliant label persistence via a labels.jsonl file in the wallet data directory.
• Label column in unspent and transactions output (both --pretty and JSON).
• parse_txid helper in utils.rs.
• bip329 = "0.4.0" dependency in Cargo.toml.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature
• I've updated CHANGELOG.md

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[Musab1258]

Hi @tvpeter, I am done with this. You can check it out when you are free.

I will start working on the follow-up PR to add import and export of label files.

[Musab1258]

Hi @tvpeter, I eventually decided to add the import and export of BIP-329 JSONL files' implementation here when, after I was done with the implementation, I saw that it was something that could fit into this PR without bloating it.

So, instead of creating a second PR and having reviewers go through the stress of reviewing two PRs that can probably fit into one, I decided to make it one PR.