runtests: assume Time::HiRes, drop Perl Win32 dependency

`Time::HiRes` was already used unconditionally before this patch in
`servers.pm`. This package, and functions used by runtests (`sleep` and
`gettimeofday`) are supported by the minimum Perl version required for
curl:

https://perldoc.perl.org/5.8.0/Time::HiRes

- Drop the `portable_sleep()` wrapper in favor of `Time::HiRes::sleep()`.
- Use `Time::HiRes` unconditionally in `serverhelp.pm`.
- Stop using the `Win32` package where available. It was included
  to provide a Windows fallback for `Time::HiRes::sleep()`. It was never
  actually called, but the dependency may have loaded `Win32.dll`, which
  often appears in failed fork operations in GHA logs.
  Ref: a6fed41f6f #5054 #5034
  Ref: https://github.com/curl/curl/discussions/14854

Closes #18287

tests/serverhelp.pm

@@ -29,6 +29,8 @@ package serverhelp;
 use strict;
 use warnings;
 
+use Time::HiRes;
+
 BEGIN {
     use base qw(Exporter);
 
@@ -52,13 +54,6 @@ BEGIN {
         datasockf_pidfilename
         datasockf_logfilename
     );
-
-    # sub second timestamping needs Time::HiRes
-    eval {
-        no warnings "all";
-        require Time::HiRes;
-        import  Time::HiRes qw( gettimeofday );
-    }
 }
 
 use globalconfig;
@@ -81,20 +76,10 @@ our $logfile;  # server log file name, for logmsg
 # logmsg is general message logging subroutine for our test servers.
 #
 sub logmsg {
-    my $now;
-    # sub second timestamping needs Time::HiRes
-    if($Time::HiRes::VERSION) {
-        my ($seconds, $usec) = gettimeofday();
-        my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
-            localtime($seconds);
-        $now = sprintf("%02d:%02d:%02d.%06d ", $hour, $min, $sec, $usec);
-    }
-    else {
-        my $seconds = time();
-        my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
-            localtime($seconds);
-        $now = sprintf("%02d:%02d:%02d ", $hour, $min, $sec);
-    }
+    my ($seconds, $usec) = Time::HiRes::gettimeofday();
+    my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
+        localtime($seconds);
+    my $now = sprintf("%02d:%02d:%02d.%06d ", $hour, $min, $sec, $usec);
     # we see warnings on Windows run that $logfile is used uninitialized
     # TODO: not found yet where this comes from
     $logfile = "serverhelp_uninitialized.log" if(!$logfile);