test: add testListenersOrder

[phil-davis]

This tests the change in #162 that makes sure not to sort listeners that are of equal priority, but to preserve the order in which they were created.

I ran these unit tests against the old code, and as expected, one of the test cases fails. The old code used to, somewhat accidentally, sort the events with the same priority into alphabetical order. We don't want or expect that to happen any more.

$ composer phpunit
PHPUnit 11.5.56 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.3.32
Configuration: /home/phil/git/sabre-io/event/tests/phpunit.xml

................................................................. 65 / 88 ( 73%)
......F................                                           88 / 88 (100%)

Time: 00:01.496, Memory: 10.00 MB

There was 1 failure:

1) Sabre\Event\WildcardEmitterTest::testListenersOrder with data set #1 ('bMethod', 'aMethod')
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
     0 => Array (
         0 => Sabre\Event\WildcardEmitterTest Object ()
-        1 => 'bMethod'
+        1 => 'aMethod'
     )
     1 => Array (
         0 => Sabre\Event\WildcardEmitterTest Object ()
-        1 => 'aMethod'
+        1 => 'bMethod'
     )
 )

/home/phil/git/sabre-io/event/tests/Event/WildcardEmitterTest.php:67

FAILURES!
Tests: 88, Assertions: 144, Failures: 1.
Script phpunit --configuration tests/phpunit.xml handling the phpunit event returned with error code 1

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.17%. Comparing base (03ea383) to head (d985ad0).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #172   +/-   ##
=========================================
  Coverage     99.17%   99.17%           
  Complexity      111      111           
=========================================
  Files             7        7           
  Lines           364      364           
=========================================
  Hits            361      361           
  Misses            3        3           

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