This changeset reduces the socket read chunk size for queries over TCP/IP to a reasonable value of 64 KiB. PHP's fread() uses an underlying read() call with the given chunk size (defaults to 8 KiB) instead of the size limit given to the fread() call. In an attempt to address a race condition on Mac, I've accidentally raised this default chunk size to 2 GiB via #172/#177. This means that any socket read would temporarily consume 2 GiB of memory, even if we only read a few bytes of data. Ouch.

With these changes applied, the test suite now reports a memory usage of ~84 MB instead of 8 GB(!). I've only stumbled upon this recently while addressing PHP 8.1 compatibility (#188) and trying to execute this with PHP's default memory_limit of just 128 MiB. The good news is this didn't usually happen during normal operation, as the TCP/IP transport will only be used as a fallback if the UDP query returns a truncated message.