Stop using deprecated `github.com/pkg/errors` module

# Summary

The `github.com/pkg/errors` module is no longer supported and has been archived. Depending on archived/unsupported libraries is generally a bad practice. The only feature the package added to the standard library was collecting stack traces.

# Resolutions

1. Copy the sources from `github.com/pkg/errors` into the EKSA code base.
2. Depend on a different library.
3. Use the std lib only and accept we won't get stack traces.

The issue does not name any files, tests, or entry points. Start by locating EKSA's uses of github.com/pkg/errors and reviewing the dependency configuration, then determine which of the three listed resolutions is accepted. Done means the archived module is no longer used and the chosen error-handling behavior is covered by the relevant existing checks.

Written by the indexing model from the issue text.