Load the Favorite TV guide on focus instead of every 5 minutes

[silentbil]

Why

While Home was open, the Favorite TV row asked the network for guide data every 5 minutes. With an XMLTV source there is no per-channel request, so every tick downloaded the whole guide file — all day and all night on an idle TV — for now/next text that is only shown on a focused card.

What changed

• The periodic Favorite TV EPG timer is removed.
• When focus reaches the Favorite TV row, now/next is re-derived from the saved guide (at most once a minute).
• The network is asked only while the saved guide has no current programme for one of the row's channels, and at most every 30 minutes.
• The TV screen's own guide loading is unchanged.

Testing

• New FavoriteTvGuideRefreshTest for the network and focus throttling rules; existing Home tests pass.
• On an Android TV emulator with an XMLTV playlist: Home left idle for 13 minutes made 0 guide requests (previously the first came after ~11 minutes, then every 5). Focusing the row made one request (the saved guide was stale) and the cards then showed correct Now/Next; moving along the row made no further requests.