Optimize package search

[alexkuz]

• call installer.get_description() with for_search=True for faster search (I'm not 100% sure what's the difference in terms of searching but it seems appropriate and the performance gain is very noticeable*)
• cache name, summary, description etc. for each package for faster consequent searches
• pre-generate search cache in background when installer is ready
• reset page to landing if search input is empty
• cancel current search if user navigated back to landing
• minor performance improvements (iterate through packages without redundant allocations)

UPD:

• improve search performance more with CooperativeIterator
• show progress bar on package search instead of spinner

Before	After
simplescreenrecorder-2025-06-01_13.42.01.mp4	simplescreenrecorder-2025-06-01_13.27.04.mp4

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*) 12s vs 200s on my machine