Subscriptions: use experiment cohort for performance optimized paywalls

[shakyShane]

Task/Issue URL: https://app.asana.com/1/137249556945/task/1219056538070932
Related Privacy Config PR: duckduckgo/privacy-configuration#6002
Tech Design URL (if applicable):
API Proposals URL(s) (if applicable):

Description

• now uses the 'cohorts' support from privacy config to enable a 50/50 split of performanceOptimizedPaywalls
  • this helps to solve an attribution problem I would've had, where the impact of the performance work might have been under counted because of the way I was going to use the new vs old paths + clicks as the metric.

Steps to test this PR

Unsupported - this proves the change makes no difference to old app users

• tap 'VPN' or other entry point
• verify the URL used is the regular format like /subscriptions?featurePage=duckai
• verify it DOES NOT include the experiment param experiment_perfpaywall

---

Supported - this proves the change will take effect when minSupportedVersion is eventually used in the remote config

• I used a version of the remote config PR with this patch

  Index: overrides/android-override.json
  IDEA additional info:
  Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
  <+>UTF-8
  ===================================================================
  diff --git a/overrides/android-override.json b/overrides/android-override.json
  --- a/overrides/android-override.json	(revision d34b3045e90cc5d27691c615d5f13a31c8040d75)
  +++ b/overrides/android-override.json	(date 1790861563871)
  @@ -4509,7 +4509,7 @@
                       }
                   },
                   "performanceOptimizedPaywalls": {
  -                    "state": "disabled",
  +                    "state": "enabled",
                       "cohorts": [
                           {
                               "name": "control",
  

• tap 'VPN' or other entry point

• verify the URL used is the new format like /subscriptions/new/mobile/duckai

• verify it DOES include the experiment param experiment_perfpaywall=control|treatment

---

cohort	path + query
unsupported	/subscriptions?origin=funnel_appmenu_android
control	/subscriptions/new/mobile/vpn?origin=funnel_appmenu_android&trial=true&pir=false&experiment_perfpaywall=control
treatment	/subscriptions/new/mobile/vpn?origin=funnel_appmenu_android&trial=true&pir=false&experiment_perfpaywall=treatment

---

[shakyShane]

NOTE: this is a DRAFT. I am updating the description with testing steps shortly. :)

[claude]

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[Kyriakos-Georgiopoulos]

@claude review

[claude]

Code review found no issues

No high-confidence issues detected in this change.