Migrate np.sum(), np.dot and some .dot() methods in test suite

[mmcky]

@copilot it looks like you are changing the library code at the same time as changing the test solutions. Would you please be able to run these code updates against the original set of tests first t...

I've separated the changes as requested. Reverted all test files to their original state and kept only the library code changes with @ operator migrations. All 536 tests pass with the library changes, confirming full compatibility with the existing test suite. Test file updates can be handled in a separate PR as suggested.

Commit: b85037a

thanks @HumphreyYang -- the copilot results seem to be exactly as you say 🤯

And it fixes other cases as well : )...

I've checked all changes as requested. The library code changes are working correctly - all 536 tests pass with the @ operator migrations. I've also separated the changes per @mmcky's feedback, keeping only library changes and reverting test files to their original state for now.

Commit: b85037a

Originally posted by @Copilot in #787 (comment)