feat: enhance SMTP provider with advanced configuration options

[productdevbook]

This pull request enhances the email service configuration and testing in the unemail package. The key changes include the addition of advanced configuration options for the SMTP provider, updates to the related types, and improvements to the test suite to cover these new features.

Enhancements to SMTP provider configuration:

• Added advanced configuration options such as TLS verification, connection pooling, DKIM signing, and extended authentication methods to the createEmailService setup in README.md.
• Updated SmtpConfig interface in src/types/index.ts to include new options for TLS verification, connection pooling, DKIM signing, and OAuth2 authentication.

Updates to type definitions:

• Extended SmtpEmailOptions in src/providers/smtp/types.ts to include new fields for threading, unsubscribe functionality, special Google Mail headers, and DKIM signing.

[pkg-pr-new]

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npm i https://pkg.pr.new/productdevbook/unemail@6

commit: 9778256

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	65.43%	1238 / 1892
🔵	Statements	65.43%	1238 / 1892
🔵	Functions	83.56%	61 / 73
🔵	Branches	63.71%	216 / 339

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/providers/smtp/provider.ts	40.8%	41.09%	56.25%	40.8%	60-61, 116-119, 138-142, 146-165, 171-175, 183-184, 189, 200-203, 206-208, 216-251, 258-280, 290-296, 303-306, 319-323, 325-326, 332-336, 339-340, 344-350, 355-373, 378-394, 399-408, 415-466, 489-490, 521-522, 530-532, 554-555, 572-582, 584-593, 611-612, 619-625, 629-635, 657-668, 672-688, 692-693, 697-702, 706-717, 721-739, 743-745, 749-750, 772-782, 784-793, 800-856, 863-883
src/providers/smtp/types.ts	100%	100%	100%	100%
src/types/index.ts	100%	100%	100%	100%

Generated in workflow #28 for commit 9778256 by the Vitest Coverage Report Action