[php-src] Issue #18869: Poor performance shmop read

Issue: https://github.com/php/php-src/issues/18869 Author: remco-pc ### Description i've tried to use the shmop functions for a large file (json) (4GB) and have save it in chunks of around 4 MB each. With this approach i tried to read it and got poor performance; around 200 Mbit/sec only where i expected at least around 10x faster. The chunks cannot be really big currently and i wonder why that is, because if you could do chunks of hundreds of megabyte it would be faster as my current ramdrive which reads at 2.5 GB/sec with a file read (from tmpfs ramdrive) This was in wsl2 on windows11 ### PHP Version ```plain Php 8.3.22 (cli) ``` ### Operating System Debian 12