Fix compilation errors in main.rs

[linksplatform-sweepai]

Description

This PR fixes the compilation errors in main.rs that were reported in issue #7. The errors were related to the Link type not being found in the scope and the placeholder _ not being allowed within types on item signatures for functions.

Summary of Changes

• Added an import statement to import the Link struct from the doublets crate in main.rs.
• Replaced the placeholder _ with a type parameter in the function signature of get_link_by_id in main.rs.

Fixes #7.

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