🔊 [RUMF-1577] Collect page lifecycle states

[amortemousque]

Motivation

Modern browsers today will sometimes suspend pages or discard them entirely when system resources are constrained, which can lead to unexpected behaviors. The Page Lifecycle API, provides lifecycle hooks so we can detect and handle these browser interventions.

This PR, collect page lifecycle state changes during a view to help Browser SDK issue investigations.

Changes

• Value history findAll accepts a duration
• Add maxEntries limit to valueHistory
• Use valueHistory in pageSateHistory
• Collect page states changes during views
• Limit the number of page states collected per view

Testing

• Local
• Staging
• Unit
• End to end

---

I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

Merging #2229 (273911e) into main (0a0e00a) will increase coverage by 0.06%.
The diff coverage is 95.00%.

@@            Coverage Diff             @@
##             main    #2229      +/-   ##
==========================================
+ Coverage   94.01%   94.07%   +0.06%     
==========================================
  Files         201      201              
  Lines        6083     6095      +12     
  Branches     1347     1349       +2     
==========================================
+ Hits         5719     5734      +15     
+ Misses        364      361       -3     

Impacted Files	Coverage Δ
...s/rum-core/src/domain/contexts/pageStateHistory.ts	93.02% <92.68%> (+10.09%)	⬆️
packages/core/src/tools/experimentalFeatures.ts	100.00% <100.00%> (ø)
packages/core/src/tools/valueHistory.ts	100.00% <100.00%> (ø)
packages/rum-core/src/boot/startRum.ts	92.00% <100.00%> (+0.16%)	⬆️
.../domain/rumEventsCollection/view/viewCollection.ts	100.00% <100.00%> (ø)
packages/rum-core/test/testSetupBuilder.ts	96.05% <100.00%> (+1.31%)	⬆️

... and 1 file with indirect coverage changes

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[BenoitZugmeyer]

🥜 nitpick: ‏It could be easier to grasp as:

for (let index = pageStateEntries.length - 1; index >= 0 && pageStateServerEntries.length < maxPageStateEntriesSelectable; index--) {
}

Or, maybe you could adapt the previous version as: .findAll().slice(0, maxPageStateEntriesSelectable).reverse().map()

[amortemousque]

Hum, I was hesitating to do that in the first place but as it is less effective performance wise I went with a good old loop. I don't have a strong opinion though. Maybe a third party @bcaudan can help deciding?

[bcaudan]

I had the same thought, maybe adding a couple comments could make this code easier to grasp while keeping the most performant approach.

[amortemousque]

I've added some comments:

browser-sdk/packages/rum-core/src/domain/contexts/pageStateHistory.ts

Lines 84 to 88 in 6f8127f

	// limit the number of entries to return
	const limit = Math.max(0, pageStateEntries.length - maxPageStateEntriesSelectable)
	// loop page state entries backward to return the selected ones in desc order
	for (let index = pageStateEntries.length - 1; index >= limit; index--) {