fix(core): delay zero-cache eviction until LA resolutions drain

[jmaeagle99]

What was changed

The zero-sized-cache eviction in WFStream::process_completion now also skips runs that still have jobs queued for lang, not just runs still waiting on local activities. This defers the eviction rather than skipping it since process_completion is called for every completion; the last completion will not have pending jobs nor outstanding LAs, thus the eviction is queued.

Why?

With max_cached_workflows = 0 and local activities, a run could be evicted mid-workflow-task, stranding its LA markers and livelocking the workflow.

#1442 delivers LA resolutions incrementally, so a resolution arriving while an earlier one is still outstanding with lang is parked as a pending job. That creates a state which didn't exist before that change: no outstanding LAs, but resolutions still undelivered. So the eviction landed mid-task: the accumulated RecordMarker commands were
discarded with the run and the WFT was never reported. Task timeout occurs and server redelivers the WFT; the same run is replayed, same local activities, same result, repeated indefinitely.

On debug builds, like in CI, a panic is intentionally raised with the message There should not be any outgoing commands or messages when preparing a completion response if the activation was only an eviction. This is an SDK bug..

Checklist

1. How was this tested: New explicitly-driven core test and locally with sdk-python submodule update

2. Any docs updates needed? No