fixes #26050; preserve defer scope across when nimvm

[subotac]

Fixes #26050.

Preserve the enclosing statement-list tail when lifting defer from when nimvm branches, so the deferred action runs at the end of the lexical scope in both native and VM execution.

Adds native and VM regression coverage.

[Araq]

Adhoc logic, there's got to be a better way.

[subotac]

Agreed — I reworked this to split the same-scope control flow around each defer, including through retained when nimvm nodes. The conditional portions stay under when nimvm, while the surrounding continuation remains shared. This avoids copying the outer tail into both branches and also covers nested and multiple defers.