perf(tests): enforce PHPUnit time limits with sensible timeout values

The timeout attributes were defined but never enforced because
enforceTimeLimit was missing. Adds enforceTimeLimit="true" and reduces
values from the 900s blanket default to 60s/300s/600s for
small/medium/large tests. Unannotated tests default to medium (300s),
cutting the worst-case hang time per test from 15 min to 5 min.

Signed-off-by: Anna Larch <anna@larch.dev>
AI-Assisted-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Anna Larch <anna@nextcloud.com>

Author: Anna Larch

tests/phpunit-autotest-external.xml

@@ -6,9 +6,10 @@
 -->
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 		 bootstrap="bootstrap.php"
-		 timeoutForSmallTests="900"
-		 timeoutForMediumTests="900"
-		 timeoutForLargeTests="900"
+		 enforceTimeLimit="true"
+		 timeoutForSmallTests="60"
+		 timeoutForMediumTests="300"
+		 timeoutForLargeTests="600"
 		 cacheDirectory=".phpunit.cache"
 		 xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd">
 	<testsuite name="Nextcloud files external">

tests/phpunit-autotest.xml

@@ -6,9 +6,10 @@
 -->
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 		 bootstrap="bootstrap.php"
-		 timeoutForSmallTests="900"
-		 timeoutForMediumTests="900"
-		 timeoutForLargeTests="900"
+		 enforceTimeLimit="true"
+		 timeoutForSmallTests="60"
+		 timeoutForMediumTests="300"
+		 timeoutForLargeTests="600"
 		 cacheDirectory=".phpunit.cache"
 		 xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd">
 	<testsuite name="Nextcloud Server">