Context::take rejects active snapshots by requiring GPU pages for zero-copy working-page transfer

[evanc7007]

ContextManager::take() appears to have an allocation mismatch for active/on-GPU snapshots.

For active snapshots, take() estimates that zero new GPU pages are needed because snapshot working pages should be transferred directly into the new context. However, take_inner() then unconditionally requires snap.working_pages.len() pre-allocated GPU pages, causing take() to fail for active snapshots that have working pages.

Relevant file:

runtime/src/context/snapshot.rs