feat: add SMTP provider implementation and example usage

[productdevbook]

SMTP Provider

import { createEmailService } from 'unemail'
import smtpProvider from 'unemail/providers/smtp'

const emailService = createEmailService({
  provider: smtpProvider({
    host: 'smtp.example.com',
    port: 587,
    secure: false, // use TLS
    user: 'username',
    password: 'password'
  })
})

// With advanced options
await emailService.sendEmail({
  from: { email: '[email protected]', name: 'Sender' },
  to: { email: '[email protected]' },
  subject: 'Test email',
  text: 'Plain text content',
  html: '<p>HTML content</p>',

  // SMTP-specific options
  priority: 'high', // 'high', 'normal', or 'low'
  dsn: {
    success: true, // Request successful delivery notification
    failure: true, // Request failure notification
    delay: true // Request delay notification
  }
})

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	66.61%	1261 / 1893
🔵	Statements	66.61%	1261 / 1893
🔵	Functions	84%	63 / 75
🔵	Branches	68.03%	215 / 316

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/providers/smtp/index.ts	100%	100%	100%	100%
src/providers/smtp/provider.ts	23.47%	63.63%	25%	23.47%	42-79, 85-124, 130-142, 148-191, 214-215, 241-258, 278-423, 425-434, 441-469
src/providers/smtp/types.ts	100%	100%	100%	100%

Generated in workflow #14 for commit 6e1f9d3 by the Vitest Coverage Report Action