[Performance] Optimize linesToColumns in string utilities

[gonzaloriestra]

WHY are these changes introduced?

The linesToColumns utility function in packages/cli-kit is used to format CLI output into aligned columns. The previous implementation was inefficient because it:

1. Called unstyled(row).length twice for every cell (once for width calculation and once for padding). Since unstyled uses regex to strip ANSI escape codes, this is relatively expensive.
2. Performed multiple redundant O(Cols * Rows) array mappings to calculate max widths and row lengths.

WHAT is this pull request doing?

This PR optimizes linesToColumns by:

• Refactoring the column width calculation to use a single pass over the data.
• Caching unstyled lengths in an intermediate structure, reducing calls to the expensive unstyled utility by 50%.
• Eliminating redundant array mappings and intermediate array creations.

How to test your changes?

Run the following command to verify that the string utility tests still pass:
pnpm --filter @shopify/cli-kit vitest run src/public/common/string.test.ts

Duplicate check

Query: gh pr list --repo Shopify/cli --state all --limit 200 --search 'label:"Jules" "Performance" in:title' --json number,title,state,url,body,files
Fallback: git log --grep="\[Performance\]" --oneline

Closest prior PRs:

1. 9d50d23b6 [Performance] Optimize crypto utility functions: Optimized crypto helpers but didn't touch string utilities.
2. 024fbcaf5 [Performance] Optimize Liquid template rendering: Optimized template rendering logic.
3. a1c7666c9 [Performance] Optimize CLI startup and project discovery: Optimized project discovery and file system loading.

This PR is meaningfully different because it targets core string formatting logic in packages/cli-kit/src/public/common/string.ts, which was not addressed in previous performance PRs.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch) and added a changeset with pnpm changeset add (Note: internal optimization, skipped changeset as per standard performance task scope)

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PR created automatically by Jules for task 6574077092894988872 started by @gonzaloriestra

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