fix: fix incorrect path substitution in sed command

[defitricks]

Description

There was a missing / after $input_dir in the sed command, which could result in incorrect path substitution. If the path started with $input_dir but contained subdirectories, the replacement might not work as expected.

Now, the command explicitly matches the beginning of the string using ^ and ensures $input_dir/ is properly removed.

How Has This Been Tested?

Tested by running the modified command with various input paths, including cases with and without subdirectories. The results now correctly remove $input_dir/ only when it appears at the beginning of the path.

Checklist:

Before deployment

• 100% test and branch coverage
• check slither for severe issues
• fuzz and invariant tests (when applicable)
• formal verification (when applicable)
• deployment or upgrade scripts ready

After deployment

• transfer ownership after deployments (when applicable)
• complete upgrade (when applicable)
• generate deployment/upgrade log files

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Considerations

• I have followed the contributing guidelines.
• My code follows the style guidelines of this project and I have run forge fmt and prettier to ensure the code style is valid
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Additional context

Verification

For example, given:

input_dir="src/pkgs/example"
sol_file="src/pkgs/example/contracts/MyContract.sol"

The original sed command would produce:

contracts/MyContract.sol

However, without / after input_dir, it could produce incorrect results if the path structure is more complex.