refactor(core,keys): BIP-39's English list moves into halkyon_core

The list a recovery phrase's words are of moves from halkyon_keys into
halkyon_core, exported as bip39English, so that the server module can
take a waiting account's matching code from it (Halkyon Learn's ADR
0021, D33) without depending on halkyon_keys and libsodium. Its test
(2048 words, sorted, the published file's SHA-256, unique by their first
four letters) moves along; its MIT licence too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_core/lib/halkyon_core.dart

@@ -6,6 +6,8 @@
 /// - A `Logger` interface and basic `ConsoleLogger` implementation.
 /// - The optional `HalkyonException` marker interface.
 /// - `SerialQueue` and `CoalescingRunner`, which run work one at a time.
+/// - BIP-39's English word list (`bip39English`), which a recovery phrase's
+///   words and an account's matching code are of.
 library;
 
 // Re-export the clock package directly. Halkyon apps depend on `Clock` for
@@ -15,6 +17,7 @@ export 'package:clock/clock.dart' show Clock, clock;
 
 export 'src/async/coalescing_runner.dart';
 export 'src/async/serial_queue.dart';
+export 'src/bip39_english.dart';
 export 'src/exceptions.dart';
 export 'src/logger.dart';
 export 'src/uuid.dart';