Fix used memory reporting

[staabm]

while observing memory consumption of PHPStan I noticed a difference between what PHPStan reports as "used memory" and what the operating system resource monitor reports.

especially in the last few seconds of the phpstan run, I noticed a climb in the very end, which was not at all reflected.

running php phpstan analyse -c myphpstan.neon.dist -vvv --debug on my example projects

... before this PR ends in

...
C:\dvl\Workspace\motiontm\models\_Images.php
--- consumed 0 B, total 624 MB, took 0.00 s
C:\dvl\Workspace\motiontm\public\partner\index.php
--- consumed 0 B, total 624 MB, took 0.00 s
Result cache is saved.

 [OK] No errors

Used memory: 624 MB

the end-memory result seems identical with what was reported in the last "consumed"-line. the consumption itself is pretty accurate while running but only a climb up to ~690 at the very end is missing.

---

After this PR I am taking the memory-peak of the master process into account right before printing the message.
With this change I am now getting something like

...
--- consumed 0 B, total 624 MB, took 0.00 s
C:\dvl\Workspace\motiontm\public\partner\index.php
--- consumed 0 B, total 624 MB, took 0.00 s
Result cache is saved.

 [OK] No errors

Used memory: 692 MB

which matches pretty good what I am getting from the operating system.
note the difference between the "used memory" metric and the one of the last "consumed" line

[phpstan-bot]

This pull request has been marked as ready for review.

[ondrejmirtes]

Thank you.