Use {{#each}} key to provide component stability for AiAssistantPastSessionsList

[habdelra]

The issue here is that in the host/app/components/ai-assistant/panel.gts module, the AiAssistantPanel.aiSessionsRooms getter. Specifically this getter returns a different array instance each time it's recomputed so that there is no component stability for the AIPastSessionsList component that consumes this as an argument. each time there is a matrix event that is received (which happens via the /sync calls), a wholly new array is created, and hence the AIPastSessionsList component's {{#each}} is re-rendered for all the items in the array. The solution is to use the key property of the {{#each}} helper to guide ember on how to stabilize the rerenders, so that it knows what is new and what is the same in the array.

Before:

After:

[github-actions]

Host Test Results

    1 files  ±0      1 suites  ±0   21m 11s ⏱️ +20s
679 tests ±0  678 ✔️ ±0  1 💤 ±0  0 ❌ ±0 
684 runs  ±0  683 ✔️ ±0  1 💤 ±0  0 ❌ ±0 

Results for commit 90aea70. ± Comparison against base commit a7d4a87.