perf: reduce allocations in the printer and string-list sorting

[jbedard]

Buildtools PR checklist

• The code in this PR is covered by unit/integration tests.
• I have tested these changes and provide testing instructions below.
• I have either responded to, or resolved all Gemini comments on the PR.
• I have read Google Eng Practices on Small Changes, this PR either follows these guidelines or the description provides reasoning for why they can not be followed.

Description

Reduce array copying to only when necessary, which seems like the exception and not the norm.

[gemini-code-assist]

Code Review

This pull request optimizes the seq method in build/print.go by only copying the argument slice when a nil element is present. The reviewer suggested a further optimization to avoid a full second pass over the slice by copying the non-nil prefix and iterating only over the remaining elements.

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[oreflow]

Cleaning up past reviewers due to lack of capacity, and buildtools were now moved to be bazel-contrib community supported.