A zlib compressed stream may have a CRC32 checksum instead of Adler-32 which the PHP gzuncompress() function expects. Add a second zlib decompression attempt if the first one fails. See: https://www.php.net/manual/en/function.gzuncompress.php#79042
Partially resolves smalot#592.

Instead of setting an error handler to catch the E_WARNING's that gzuncompress() emits, suppress it with an @ so we can do away with the try/catch. Make a note of this in the comments.
Switch from using tempnam() to tmpfile() because tempnam() can emit E_NOTICE's and would have to be suppressed as well. tmpfile() just returns a handle or false.
Limit file_get_contents() by the $decodeMemoryLimit. Unlike gzuncompress() for which a limit value of zero (0) means "no limit", file_get_contents() takes null to mean "no limit".

Fix for PHP < 8.0 that doesn't like a length limit of null for file_get_contents().