Disable zend.assertions as suggested by PHPParser - #6021

nikic/PHP-Parser Performance.markdown suggests to use zend.assertions=0 at runtime.

at best the php.ini of the php binary beeing used would define zend.assertions=-1, but thats neither the default php ships with in development nor is it likely people will adjust this setting in a environment in which PHPStan is running

quoting the php.ini:

; Switch whether to compile assertions at all (to have no overhead at run-time)
; -1: Do not compile at all
;  0: Jump over assertion at run-time
;  1: Execute assertions
; Changing from or to a negative value is only possible in php.ini!
; (For turning assertions on and off at run-time, toggle zend.assertions between the values 1 and 0)
; Default Value: 1
; Development Value: 1
; Production Value: -1
; https://php.net/zend.assertions
;zend.assertions = -1

so with this PR we disable zend-asserts at runtime in case they are not disabled entirely by the used php.ini setting already.

testing on https://github.com/TomasVotruba/php-parser-speed-comparison-2026 suggests this has some small benefit