Make copy selection report failure without selection

[catlover-bot]

Summary

Make CopySelection and CopySelectionSystem report whether they actually had a selection to copy, and propagate that status through ReedlineEvent::Edit so UntilFound can continue when there is no active selection.

This follows the direction discussed in #876 of making edit operations explicit about their success/failure state. This PR intentionally limits that behavior to the two copy-selection commands; broader edit-command status semantics and ExecuteHostCommand are out of scope.

Observable behavior changes only for UntilFound chains containing CopySelection or CopySelectionSystem.

Before

ReedlineEvent::Edit was always treated as Handled, even when CopySelection or CopySelectionSystem had no active selection. As a result, an UntilFound chain stopped at the copy command and never tried a fallback event such as CtrlC.

After

CopySelection and CopySelectionSystem return failure when no selection is active. ReedlineEvent::Edit converts that result to EventStatus::Inapplicable, allowing UntilFound to try the next event. When a selection exists, the copy command remains handled and the chain stops as before.

Regression tests cover both copy commands with and without an active selection.

Additional notes

Addresses the CopySelection / CopySelectionSystem portion of #876.

Validation performed locally:

• cargo fmt --all -- --check
• cargo clippy --locked --all-targets --all-features
• cargo test --all --all-features -- --test-threads=1 (1528 passed, 1 ignored; doctests: 30 passed)
• git diff --check

A local cargo nextest run --all --all-features hang was observed in deferred-completion tests. The same class of tty cursor-query hang is being addressed separately in #1156, and the affected test passes immediately under cargo test --all-features.