align small PHP compatibility behaviors

[vapebw]

In php 8.x, several standard library behaviors differ from zphp in small but observable compatibility cases:

• array_rand($array, 1) returns a scalar key, just like omitting the second argument
• array_diff() / array_intersect() and their key/assoc variants accept a single array and return it unchanged
• date_get_last_errors() is available as the procedural alias of DateTime::getLastErrors()

Previously:

• array_rand($array, 1) returned a one-element array instead of a scalar key
• single-array diff/intersect calls returned null
• date_get_last_errors() was not registered even though the underlying implementation already existed

Solution

• Return the scalar-key path whenever array_rand() receives num == 1
• Allow arraySetOp() to operate with a single array, reusing the existing empty comparison logic
• Register date_get_last_errors() using the existing dtGetLastErrors implementation

Tests

• Added coverage for array_rand() with omitted, 1, and multiple-key counts across string and integer keys
• Added parity coverage for single-array array_diff, array_intersect, _key, and _assoc variants
• Added coverage for date_get_last_errors() availability and consistency with DateTime::getLastErrors() / DateTimeImmutable::getLastErrors()

[TrixNEW]

LGTM 👍