Rebuild the test suite: one class per element variation

Problem/Motivation

The current tests are one Functional class with four methods and one Unit class that still uses doc-comment metadata, which PHPUnit 12 removes. The Functional assertions compare exact HTML strings, so core markup changes break them for no reason. Nothing covers tampered input, #states, machine_name, disabled keys, hidden children or the cardinality clamps, and the test module routes are open to everyone if it is enabled by mistake.