fix: finalize metrics for unexecuted tasks (#739)

[sesteves]

Summary

• When a worker channel ends without a final report, complete the planned task with an empty metrics or dynamic-filter report.
• Skip plan-node metric rewriting for unexecuted tasks rather than inventing execution metrics.
• Enable the regression test from fix: add ignored regression test for metrics finalization (#739) #751 and verify both rewrite paths after an AQE task is left unexecuted. Static and adaptive planning share this coordinator receive path.

Tested on devspace: 15 metrics integration tests, four dynamic-filter integration tests, and two dynamic-filter display unit tests pass; formatting passes.

Fixes #739

[gabotechs]

Nice! thanks @sesteves, just left some cosmetic suggestions, but this looks good.

[gabotechs]

Thanks @sesteves!