clean resources (sockets/files)

[ajozwik]

As a result of investigating the unstable tests, the following issues were discovered:

• After tests on linux the some sockets are waiting for close(even 10 minutes after run):

netstat -nap | grep tcp | grep ps ax | grep sbt | grep java | awk '{print $1}'
tcp6      32      0 127.0.0.1:36046         127.0.0.1:39005         CLOSE_WAIT  28290/java
tcp6       0      0 127.0.0.1:52832         127.0.0.1:41039         CLOSE_WAIT  28290/java
tcp6       0      0 127.0.0.1:37852         127.0.0.1:33087         CLOSE_WAIT  28290/java

Tested on ubuntu 25 and slackware 15.

But it failed unpredictably - so solution was removed from this PR

After adding ServerWebSocketTests.scala waitForMessage the problem disappeared.

• For other if StreamMaxLengthExceededException/EntityStreamSizeException (or related) is thrown the created file was not deleted. It is risky - this poses a risk of a DDOS attack (disk full).