[adapik]

Modern PHP code mostly initializes properties through constructor property promotion, often with readonly (DTOs, value objects, services). Every such property is a typed property without a default, so its first write always goes through zend_std_write_property().

This PR adds a fast path in ZEND_ASSIGN_OBJ for the case where the cache slot is hit, the property is IS_UNDEF with IS_PROP_UNINIT set (never unset()), and neither the property nor the object is lazy. A new zend_assign_to_uninit_typed_prop() verifies the type and stores the value.

Results (release build, callgrind over 200k constructor calls with promoted readonly properties):

• Without opcache: −24% instructions, −25% time.
• Opcache without JIT: −24% instructions, −26% time.

Two new tests cover coercion, union and class types, readonly, protected(set), hooks and lazy objects.

This PR is related to #24566 and relies on it: that fix makes sure a failed write doesn't leave the cache slot primed. Without it, this fast path would also let a first write bypass those checks. It would be best if this lands after #24566.

Follow-up to #22709.

[adapik]

Tests will be green after #24566 lands, i put this PR to draft, but it's ready for the review. I'll rebase later on.