refactor: unify conversation constructors as NewConversation with deprecated aliases

[vinodvx]

Description

Unify conversation constructors as NewConversation with deprecated aliases

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactor / chore

Checklist

• I have run make check
• I have run task examples:all
• I have run make tidy if I added or removed dependencies
• Commit messages follow conventional commits (e.g. feat:, fix:, docs:)
• I have added/updated tests for my changes
• Documentation is updated if needed

[mintlify]

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Project	Status	Preview	Updated (UTC)
agent-sdk-go	🟢 Ready	View Preview	Jul 2, 2026, 6:31 PM

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/conversation/inmem/conversation.go	50.00%	2 Missing ⚠️
pkg/conversation/redis/conversation.go	33.33%	2 Missing ⚠️

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