incrementing a register

**Type of issue**: feature request

**Impact**: API addition (no impact on existing code)

**Development Phase**: proposal

Incrementing a register (a counter) is such a common operation. Maybe we should support an increment operator:
```
cntReg += 1.U
```

No file, test, or entry point is named. Start by reviewing Chisel's register APIs and existing operator-overload handling, then determine the expected semantics for `cntReg += 1.U`. Done means the proposed syntax is supported consistently and covered by tests, but the issue's design proposal needs resolution first.

Written by the indexing model from the issue text.