fix(api): defer streaming response until referenced variables are updated

[tomerqodo]

Benchmark PR from qodo-benchmark#423

[sentry]

Bug: The blocks_variable_output method in the v1 Variable Assigner will raise a TypeError because it attempts to check for a list within a set of tuples.
_{Severity: HIGH}

Suggested Fix

Convert the assigned_selector list to a tuple before checking for its membership in the variable_selectors set. The line should be changed to return tuple(assigned_selector) in variable_selectors.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: api/core/workflow/nodes/variable_assigner/v1/node.py#L43

Potential issue: In the `blocks_variable_output` method of the v1 Variable Assigner
node, a `TypeError` will occur. The method attempts to check if `assigned_selector`,
which is a list, is a member of `variable_selectors`, which is a set of tuples. Because
lists are mutable and therefore unhashable, Python cannot perform the set membership
test and will raise a `TypeError: unhashable type: 'list'`. This will cause any workflow
to crash if it uses a v1 Variable Assigner to update a conversation variable that is
also referenced in the final answer node, breaking the feature that defers the response
until variables are updated.

_{Did we get this right? 👍 / 👎 to inform future reviews.}