refactor(pulsar-gateway): restructure csproj and improve code quality

[ducdaiii]

Summary

• Refactored .csproj structure for better maintainability
• Updated metadata fields (Description, Authors)
• Fixed potential configuration issues

Changes

1. Moved target frameworks to shared property group
2. Improved XML indentation for readability
3. Verified compatibility with BrighterTargetFrameworks

Motivation

This improves code clarity and maintainability for future contributors.

Testing

• Built successfully on .NET 6 and .NET 8
• Verified no breaking changes in integration tests

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[lillo42]

In your PR title, you are talking about the refactor, but you are trying to add pulsar, for apache pulsar we have this PR (#3682)

[iancooper]

Hi @ducdaiii, could we collaborate on #3682?

[ducdaiii]

Hi @ducdaiii, could we collaborate on #3682?

Hello, I am very willing to cooperate, it is an honor.

[codescene-delta-analysis]

Gates Passed
4 Quality Gates Passed

See analysis details in CodeScene

Quality Gate Profile: Clean Code Collective
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[iancooper]

Going to close this in favor of working on #3682