Add BIP-39 mnemonic phrase support for deterministic wallet recovery workflows

### Problem

The SDK currently exposes key primitives such as PrivateKey and PublicKey, but does not provide a mnemonic-based workflow for seed phrase generation, validation, recovery, or deterministic key derivation.
Mnemonic phrases are the standard backup and recovery mechanism across modern wallet ecosystems. Without native SDK support, developers must integrate third-party libraries and custom logic themselves, which can lead to inconsistent implementations and fragmented developer experience.
This gap also makes deterministic local development and integration testing workflows more difficult.

### Solution

**Introduce a MnemonicPhrase crypto utility that supports:**

- BIP-39 mnemonic generation
- Phrase validation and normalization
- Seed derivation with optional passphrase support
- Deterministic Ed25519 private key derivation from generated seeds
- The utility should also be exported through:
- the crypto package exports
- the top-level SDK exports

**Benefits**

- Simplifies developer onboarding
- Enables deterministic test environments
- Provides SDK-native wallet recovery workflows
- Reduces reliance on external mnemonic handling logic
- Improves consistency across applications using the SDK

**Initial Scope**

- English BIP-39 support
- Deterministic seed derivation
- Deterministic Ed25519 key derivation
- Unit tests for:
- mnemonic generation
- normalization/validation
- invalid checksum rejection
- deterministic derivation behavior

### Alternatives

_No response_