OMNISUB-7628(chore): Upgrade Flutter SDK to Play Billing 8

[cb-jit-bhuin]

Jira

https://mychargebee.atlassian.net/browse/OMNISUB-7628

Summary

• Bump chargebee-android to 2.0.0-beta-6 (now on Maven Central) and billing-ktx to 8.3.0 so consuming apps can meet Google's Play Billing 8 artifact deadline.
• Raise the Android toolchain to match Billing 8: minSdk 23, compile/target SDK 34, Kotlin 2.1.21, AGP 7.4.2, Gradle 7.6.4, JDK 17.
• Document the restore narrowing: on Android, fully expired subscriptions are no longer returned even when includeInactivePurchases is true. iOS is unchanged.

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

🗂️ Base branches to auto review (7)

• main
• master
• develop
• dev
• develop/.*
• staging/.*
• release/.*

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Enterprise

Run ID: 8939f119-0900-4045-ba88-c5faa71c19aa

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

_{Comment @coderabbitai help to get the list of available commands.}

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues
✅	Secrets	0	0	0	0	0 issues

💻 Catch issues earlier using the plugins for VS Code, JetBrains IDEs, Visual Studio, and Eclipse.