Feature: Add Promise v3 template types for all public functions. (#40 by @WyriHaximus)

All our public APIs now use Promise v3 template types to guide IDEs and static analysis tools (like PHPStan), helping with proper type usage and improving code quality:

assertType('bool', await(resolve(true)));
assertType('PromiseInterface<bool>', async(fn(): bool => true)());
assertType('PromiseInterface<bool>', coroutine(fn(): bool => true));

Feature: Full PHP 8.3 compatibility. (#81 by @clue)

Update test suite to avoid unhandled promise rejections. (#79 by @clue)