v0.18.0

• [BC BREAK] Asynit now runs on PHPUnit: bin/asynit boots PHPUnit, whose CLI, configuration, output, loggers
  and exit codes replace asynit's own. Test classes extend PHPUnit\Framework\TestCase and use its assertions.
  Asynit keeps concurrent execution and #[Depend], which now also orders PHPUnit's #[Depends]. See
  UPGRADE.md, and the Rector set in config/rector/asynit-phpunit.php for the mechanical part.
• [BC BREAK] Run settings moved to environment variables: ASYNIT_CONCURRENCY, ASYNIT_HOST, ASYNIT_TIMEOUT,
  ASYNIT_RETRY and ASYNIT_ALLOW_SELF_SIGNED_CERTIFICATE
• [BC BREAK] Drop support for PHP 8.2 and 8.3
• Fix self signed certificates being always allowed. TLS peer verification is now enabled unless
  ASYNIT_ALLOW_SELF_SIGNED_CERTIFICATE is set, so runs against a server with an untrusted certificate that used
  to pass will now fail.
• Implement the base URI (--host, now ASYNIT_HOST), which was accepted but ignored. A class configuring its
  own client with #[HttpClientConfiguration] still inherits it.
• Detect circular dependencies between tests and report them instead of failing with an unrelated error
• Fix output of concurrent tests being attributed to whichever test finished first
• Fix per test assertion counts under concurrency, which also made the detection of tests performing no
  assertion unreliable
• Fix errored and skipped tests being counted twice under concurrency
• Keep amphp and revolt frames out of stack traces when asynit is installed as a dependency