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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[gemini-code-assist]

When a nil element is found, we can optimize the filtering process by avoiding a full second pass over the entire slice. Instead, we can create the filtered slice with a length equal to the index i of the first nil element, use the highly optimized built-in copy function to copy the non-nil prefix, and then only loop over the remaining elements starting from i+1. Ensure that this optimization is consistent with the previous behavior and does not introduce any unintended side effects.

Suggested change

	args := list
	for _, x := range *list {
	// nil arguments may be added by some linter checks, filter them out because
	// they may cause NPE.
	if x != nil {
	*args = append(*args, x)
	if x == nil {
	filtered := make([]Expr, 0, len(*list))
	for _, y := range *list {
	if y != nil {
	filtered = append(filtered, y)
	}
	}
	args = &filtered
	break
	}
	}
	args := list
	for i, x := range *list {
	if x == nil {
	filtered := make([]Expr, i, len(*list))
	copy(filtered, (*list)[:i])
	for _, y := range (*list)[i+1:] {
	if y != nil {
	filtered = append(filtered, y)
	}
	}
	args = &filtered
	break
	}
	}

References

1. When modifying code, ensure that changes are consistent with previous behavior, especially if the previous behavior was intentional.