feat: add Aptos Keystore encrypted private key storage standard

Implement an encrypted credential management system based on Ethereum's
Web3 Secret Storage Definition (keystore v3), adapted for all Aptos key
types. The format is designed to be portable across Aptos SDKs.

Key features:
- Support for Ed25519, Secp256k1, and Secp256r1 private keys
- Password-based or key-file-based encryption
- scrypt (default) and PBKDF2-HMAC-SHA256 key derivation functions
- AES-128-CTR symmetric cipher via Web Crypto API
- SHA-256 MAC for password verification
- Portable JSON format for cross-SDK interoperability

New exports:
- encryptKeystore(args): Encrypt a private key to keystore JSON
- decryptKeystore(args): Decrypt keystore JSON to recover private key
- AptosKeyStore: TypeScript interface for the keystore format
- KeystorePrivateKey, KeystoreEncryptOptions: Supporting types

Includes 23 unit tests covering all key types, both KDFs, round-trip
encryption/decryption, error handling, and cryptographic verification.

Co-authored-by: Greg Nazario <greg@gnazar.io>

Author: cursoragent

CHANGELOG.md

@@ -4,6 +4,15 @@ All notable changes to the Aptos TypeScript SDK will be captured in this file. T
 
 # Unreleased
 
+## Added
+
+- Add Aptos Keystore: encrypted private key storage standard based on Ethereum's Web3 Secret Storage Definition (keystore v3)
+  - Supports all Aptos key types: Ed25519, Secp256k1, Secp256r1
+  - Password-based or key-file-based encryption using scrypt (default) or PBKDF2-HMAC-SHA256 KDFs
+  - AES-128-CTR cipher with SHA-256 MAC for password verification
+  - Portable JSON format designed for cross-SDK compatibility (TypeScript, Rust, Python, Go, etc.)
+  - New exports: `encryptKeystore`, `decryptKeystore`, `AptosKeyStore`, `KeystorePrivateKey`, `KeystoreEncryptOptions`
+
 # 6.2.0 (2026-03-22)
 
 ## Fixed

src/core/crypto/index.ts

@@ -5,6 +5,7 @@ export * from "./abstraction";
 export * from "./ed25519";
 export * from "./ephemeral";
 export * from "./federatedKeyless";
+export * from "./keystore";
 export * from "./hdKey";
 export * from "./keyless";
 export * from "./multiEd25519";