v0.4.1

What's Changed

• Add decode_and_compute_txid: decodes hex, validates the transaction, and computes the canonical txid (returns the txid, never the wtxid).
• Add is_already_known_broadcast_error: a focused, case-insensitive classifier for duplicate/already-accepted Electrum responses. - It does not turn relay-policy or invalid-transaction rejections into success.
• Rewrite broadcast_raw_tx to return the locally computed txid on a fresh broadcast and on an already-known response. Connectivity failures, unrelated broadcast rejections, invalid hex, and invalid transaction data keep their existing typed BroadcastError variants.