feat(key): add mnemonic generation and key derivation

[mkoura]

Add support for generating mnemonics and deriving extended signing keys from mnemonic sentences. Introduce KeyType and OutputFormat enums. Refactor helpers for file reading. Update KeyGroup with new methods for mnemonic and key derivation.

[Copilot]

Pull Request Overview

This PR adds comprehensive support for mnemonic generation and key derivation from mnemonic sentences to the cardano_clusterlib package. It introduces new enums for key types and output formats while refactoring file reading utilities.

• Added mnemonic generation and key derivation methods to KeyGroup class
• Introduced KeyType and OutputFormat enums for better type safety
• Refactored file reading utilities with a new generic helper function

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
cardano_clusterlib/key_group.py	Added gen_mnemonic and derive_from_mnemonic methods with comprehensive key type support
cardano_clusterlib/helpers.py	Added read_from_file helper and refactored read_address_from_file to use it
cardano_clusterlib/consts.py	Added KeyType and OutputFormat enums for type safety
cardano_clusterlib/clusterlib.py	Updated exports to include new KeyType and OutputFormat enums

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