feat(types): array element covariance into a declared array<Object> parameter

[chadmandoo]

What

A PHP array parameter is a bare array — PHP does not enforce the @param array<T> element type at runtime, so the declared element type is a hint, not a hard bound. Two cases were rejected:

final class Builder {
    /** @param list<CondI> $conditions */
    public function __construct(private array $conditions) {}
    private function mkGroup(string $op): Group { return new Group($op); }
    public function addLeaf(Leaf $c): self {
        return $this->withConditions([...$this->conditions, $c]); // spread -> Array(Mixed)
    }
    public function addGroup(string $op): self {
        return $this->withConditions([$this->mkGroup($op)]);       // method-call element
    }
}

How

• types_compatible accepts Array(Mixed) (a spread literal or an adaptive local) and an element-compatible array in either covariance direction for a declared Array(T) param — mirroring the whole-value (_, Mixed) => true trust posture, one container level down.
• array_literal_element_type_for_ir types a method-call element as Mixed instead of the syntactic Int fallback. The old fallback stored an object-returning method's result in an Array(Int) and int-cast it at the element store (a hard backend error).

Test

test_array_element_covariance_spread_and_method_call — a fluent builder using both a spread element and a method-call element into an object-element array, byte-parity vs PHP 8.5.

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