martian: replace inner mutlierror with go.uber.org/multierr

[Choraden]

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[what-the-diff]

PR Summary

• Updated Error Handling in 'fifo_group.go' and 'fifo_group_test.go' Files
  The error handling in these files has been updated to use a more efficient error management package. By changing the type and methods used for the merr variable, and updating how multiple errors are combined, the code's performance and its readability can be improved.

• Modified Test Cases in 'fifo_group_test.go' File
  The expected error strings in the test cases have been updated. We now use semicolons instead of new lines to separate the errors. This change increases the clarity and readability of the test results.

• Removal of Unnecessary Files
  The files multierror.go and multierror_test.go were removed, making the overall codebase leaner. By eliminating these unused or redundant files, we are ensuring that the codebase is clean, efficient, and easier to maintain.