Partial command matching is incorrectly suppressed by variable validation #140

Issue 1: Partial command expansion blocked by variable validation

When requesting tab-completion on a partial token, valid expansion candidates may not be shown if a sibling variable node rejects the same input during validation.

Example:

set interface h<TAB>

Expected;

hostif-0/0/0
hostif-0/0/1
...

Actual:
No expansions are displayed.

Issue 2: Partial command execution is blocked

When entering a partial command that uniquely matches a keyword, the match can be discarded if a sibling variable candidate reports a validation error.

Example:

show subscriber his
where both history and are valid alternatives.

Expected:
show subscriber history should be selected as the unique partial command match.

Actual:
'his' is not a number
is returned from the variable validation path.