Request: make DataBuilder immutable #135

Part of #103. Line numbers refer to branch chore/php-8.4-dependabot (#98). Verified = reproduced, suspected = from reading the code.

• with() / without() read like immutable withers but change the object in place, so reusing a base builder leaks changes into later variants (DataBuilder.php:29-75). Verified.
• without('x', 'y') on a missing path creates "x": null, and with(1, 'a', 'b') on a scalar a throws a raw TypeError instead of InvalidRequest (DataBuilder.php:37-40). Verified.
• with($value) without a path is silently ignored.

Breaking: code that relies on in-place mutation ($b->with(...); $b()) has to use the returned instance.