Keystore support for Import

[twblack88]

We need the ability to import keystores. Handle file upload, add password, and then decrypt.

Need to spike on the security from native store with the Mnemonic vs. plaintext. Bonus points if we can figure out how to export both the keystore & native wallet seed.

Flow with new wallet flow:
https://www.figma.com/design/om2yDg0BjLNNSkJz82O30N/Wallet-Modal?node-id=2718-94&node-type=frame&t=c3Y9ABfz37WW1oiH-11
Flow with current wallet flow:
https://www.figma.com/file/auLL8w102VUd7ypMZNDjin?node-id=75:3202&locale=en&type=design

[twblack88]

export const encryptMnemonic = (mnemonic: string, password: string): string => {
  const iv = crypto.randomBytes(16)
  const key = crypto.scryptSync(password, 'salt', 32)
  const cipher = crypto.createCipheriv('aes-256-cbc', key, iv)
  const encrypted = cipher.update(mnemonic, 'utf8', 'hex') + cipher.final('hex')
  return iv.toString('hex') + ':' + encrypted
}

const decryptMnemonic = (encryptedMnemonic: string, password: string): string | undefined => {
  try {
    const [ivHex, encryptedHex] = encryptedMnemonic.split(':')
    const iv = Buffer.from(ivHex, 'hex')
    const encrypted = Buffer.from(encryptedHex, 'hex')
    const key = crypto.scryptSync(password, 'salt', 32)
    const decipher = crypto.createDecipheriv('aes-256-cbc', key, iv)
    const decrypted = decipher.update(encrypted, undefined, 'utf8') + decipher.final('utf8')
    return decrypted
  } catch (err) {
    error('Failed to decrypt mnemonic.')
  }
}

pseudo cryptography algo to double check against thorswap, which is the biggest user of keystores (assuming AES 256 is the one)