Fix workflow prefetch asset contention

[vegaro]

Checklist

• If applicable, unit tests
• If applicable, create follow-up issues for purchases-ios and hybrids

Motivation

Workflow and offering asset pre-downloads could compete with delivery-critical workflow fetches and resolution work, delaying prefetched workflow availability.

Description

This defers offering and workflow asset pre-downloads until after workflow delivery settles, returns prefetched workflow data so assets can be warmed afterward, and gives workflow CDN fetching and workflow resolution separate dedicated dispatchers. It also clarifies AGENTS.md so agent-opened PRs default to the pr:other label unless the user explicitly requests another primary label. Tested with ./gradlew :purchases:compileDefaultsBc8DebugKotlin and ./gradlew :purchases:testDefaultsBc8DebugUnitTest --tests "com.revenuecat.purchases.common.offerings.OfferingsManagerTest" --tests "com.revenuecat.purchases.common.workflows.WorkflowManagerTest".

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.33%. Comparing base (240522e) to head (f6d3ec3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...otlin/com/revenuecat/purchases/PurchasesFactory.kt	66.66%	2 Missing ⚠️
...ecat/purchases/common/workflows/WorkflowManager.kt	90.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3649      +/-   ##
==========================================
+ Coverage   80.29%   80.33%   +0.03%     
==========================================
  Files         380      380              
  Lines       15593    15606      +13     
  Branches     2181     2183       +2     
==========================================
+ Hits        12521    12537      +16     
+ Misses       2203     2200       -3     
  Partials      869      869              

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