Plugin v3 update

[be-unkind]

Unity Engine Update:

• Unity 2020.3.48f1 -> Unity 6000.3.8f1 LTS

Unity plugin dependencies update:

• inBrain Android 2.2.0 -> 3.1.0
• inBrain iOS 2.3.0 -> 3.0.0

Breaking API changes:

• showSurveys(...) was replaced with openWall() (now accepts WallOptions as input param).
• showSurvey(...) now has additional offersEnabled param.

Bug fixes:

• Update currency sale struct conversion logic: use valid ‘endOn’ value in IOS implementation.

Demo update:

• Add separate buttons for different Wall Options (All, Surveys, Offers).

Docs update:

• Update Readme with latest API changes.

[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

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^{Security scan by Jit}