💥 remove trackBfcacheViews and track bfcache restores by default

[BenoitZugmeyer]

Motivation

trackBfcacheViews was introduced as an opt-in option because it adds a new
bf_cache loading type to view events, which could surprise customers with
existing dashboards or queries not accounting for it. It is now being promoted
to default behavior.

Changes

• Remove trackBfcacheViews from RumInitConfiguration and RumConfiguration
• BFCache restores are now always tracked when views are tracked automatically
  (i.e. trackViewsManually is not set)
• Remove track_bfcache_views from configuration telemetry serialization

Test instructions

1. Load the RUM SDK sandbox (yarn dev, http://localhost:8080)
2. Add a link to an external page in the sandbox, click it, then navigate back
3. Check RUM batches — a view event with loading_type: "bf_cache" should be present

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	170.61 KiB	170.51 KiB	-103 B	-0.06%	✅
Rum Profiler	4.74 KiB	4.74 KiB	0 B	0.00%	✅
Rum Recorder	24.91 KiB	24.91 KiB	0 B	0.00%	✅
Logs	56.38 KiB	56.38 KiB	0 B	0.00%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	127.89 KiB	127.79 KiB	-103 B	-0.08%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Pending...

🧠 Memory Performance

Pending...

🔗 RealWorld

[datadog-datadog-prod-us1-2]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 76.99% (+0.01%)

_{This comment will be updated automatically if new data arrives.
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