Rewrite the single table-driven pattern test as one focused test per
case, and add the coverage the tightened regex needs.
* Legacy lowercase-hex and the newer prefixed company_id format each get
their own positive test.
* New negatives: uppercase-hex body, a legacy body one char short, and a
new-format hex tail one char long.
* Inline each test's input and assertions; drop the shared fixture block.
Co-authored-by: Cursor <[email protected]>
