initial modernization migration

[eleith]

modernize codebase with latest best practices and tooling

1. adopted vitest and increase test coverage
2. only support node 20, 22, 24 (older versions of emailjs are required if you want node 18 support)
3. remove docjs in favor of direct typing throughout
4. add scripts for testing against a local smtp server

[Copilot]

Pull request overview

This PR modernizes the emailjs codebase by adopting Vitest for testing, restructuring code into a src/ directory with proper ES modules, and dropping support for Node.js versions older than 20. The migration removes docjs annotations in favor of direct TypeScript typing and includes comprehensive test coverage using both unit and integration tests.

Key Changes:

• Migrated from Ava to Vitest testing framework with increased test coverage
• Restructured codebase into src/ directory with modular organization
• Updated TypeScript configuration for ES2022 and NodeNext module resolution

Reviewed changes

Copilot reviewed 58 out of 63 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
vitest.config.ts	New Vitest configuration with v8 coverage provider and 80% thresholds
tsconfig.json	Updated for ES2022 target, NodeNext modules, and Vitest globals
yarn.lock	Completely removed (likely switching to package.json only)
rollup.config.ts	Removed (build process changed)
src/*.ts	New modular source structure with index, error, connection, message, etc.
src/*.test.ts	New unit and integration tests using Vitest
test/*.ts	Old Ava tests removed

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[Copilot]

Pull request overview

Copilot reviewed 58 out of 63 changed files in this pull request and generated no new comments.

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