Changes
* Add SimdJsonValueError. In php 8.0+, it extends ValueError, and it extends Error in older php versions.
This provides an API similar to the JSON module, which started throwing ValueError for invalid depths in php 8.0.
* Throw SimdJsonValueError instead of emitting notices if $depth is too small or too large in all simdjson PHP functions.
simdjson_is_valid(), simdjson_key_count() and simdjson_key_exists() now have non-null return types.
* Throw a SimdJsonException in simdjson_key_exists on error conditions such as invalid json, to be consistent with other simdjson PHP functions.
* Add an optional boolean `$throw_if_uncountable = false` to simdjson_key_count.
When this is overridden to be true, simdjson_key_count will throw a SimdJsonException if the JSON pointer refers to a value that exists but is neither an array nor an object instead of returning 0.
* Rename the parameter $assoc to $associative in simdjson_decode and simdjson_key_value, to match naming practices used in json_decode()