[enhancement] Autogeneration of cover!() for branches

### What's hard to do? (limit 100 words)

Covering every if/else branch and match arm requires a hand-written cover!() call at each site. Someone has to remember to insert each call, pick a unique label, and keep the set of covers in sync as branches are added or refactored. There is no way to say "cover all branches" and get complete, up-to-date branch/match coverage for a design.

### Current best alternative workaround (limit 100 words)

Add cover!() at the top of each branch and arm by hand, with a manually chosen label per site. This is repeated for every feature and re-reviewed after refactors, with no enforcement that a new branch got its cover or that labels stay unique. Coverage completeness depends on remembering every site, which does not scale across a large code base.

### Your view of the "best case XLS enhancement" (limit 100 words)

Have the compiler auto-insert a cover for every if/else branch and match arm, so branch/match coverage is produced automatically instead of by hand. Each synthesized cover should get a stable, unique identity that can be traced back to the source construct it measured, with no manual effort and nothing to keep in sync as control flow changes.