Fix static-analysis issues: apply hidden friend pattern to binary ope… #781

All 3 594 tests pass in 1s

8 files + 8 8 suites +8 1s ⏱️ -1s
3 594 tests +3 594 3 594 ✅ +3 594 0 💤 ±0 0 ❌ ±0
9 486 runs +9 486 9 486 ✅ +9 486 0 💤 ±0 0 ❌ ±0

Results for commit 592b68c. ± Comparison against earlier commit 6d02e75.