🧪 test(sdk): add unit tests for plugin loader

[jackby03]

Adds comprehensive unit test coverage for LoadPlugins in internal/sdk/loader.go and internal/sdk/loader_unsupported.go.

🎯 What

Adds unit test suite for internal/sdk/loader.go which previously lacked tests.

📊 Coverage

• Non-existent plugin directory returns nil, nil.
• Target path being a file returns read directory error.
• Non-.so files and directories ending with .so are ignored.
• Corrupt/non-ELF .so files return errors.
• Dynamic test plugin build and load scenarios:
  • Missing New symbol.
  • Incorrect New symbol signature/type.
  • Valid New symbol producing a valid Module.
• Partial failure handling when multiple plugins exist in a directory.
• Unsupported OS platform fallback logic (loader_unsupported.go).

✨ Result

Complete test coverage for internal/sdk plugin loader logic.

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PR created automatically by Jules for task 2167491828709477134 started by @jackby03

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