Add mnemonic string parsing, improve keystore/address handling, update README and tests

[GalaxySciTech]

Motivation

• Normalize and accept mnemonic input supplied as a single string and make mnemonic handling more robust across the codebase.
• Improve keystore validation and address derivation to account for chain-specific address formats (EVM vs non-EVM) and network/segwit metadata.
• Refresh documentation examples and Quick Start to match current APIs and recommended usage.

Description

• Add MnemonicUtil.toMnemonicCodes(String) to trim, normalize whitespace, and split mnemonic sentences and update callers to use it (Identity, WalletManager, HDMnemonicKeystore, V3MnemonicKeystore).
• Harden WalletManager keystore validation and address derivation by adding deriveAddressByChain, isBitcoinFamily, and isEvmFamily helpers and by passing chainType into keystore validation to enforce correct address checks for EVM families.
• Replace fragile String.split(" ") usages with MnemonicUtil.toMnemonicCodes and use normalized mnemonic lists when changing passwords or deriving wallets.
• Overhaul README.md to clarify features, supported chains, install instructions, quick-start runnable examples, security recommendations, and build/test commands.
• Update and add unit tests to cover the new mnemonic-string parsing and WalletManager behaviors.

Testing

• Ran the test suite with ./gradlew test and ./gradlew build in CI (Java 8/11/17 matrix); the test run completed successfully.
• Added tests MnemonicUtilTest.toMnemonicCodes_string_shouldTrimAndNormalizeWhitespace and MnemonicUtilTest.toMnemonicCodes_string_shouldRejectBlankInput, which passed.
• Added tests WalletManagerTest.findWalletByKeystore_ethereum_shouldReturnWallet and WalletManagerTest.findWalletByMnemonic_dogecoin_shouldReturnWallet, which passed.

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Codex Task