perf(minifier): use atom_from_strs_array for template literal concat

[Boshen]

Summary

• Replace 4 instances of heap String concatenation with ctx.ast.atom_from_strs_array()
• Avoids intermediate heap allocations by concatenating directly into the arena allocator
• Affects template literal merging and expression inlining into quasis

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR optimizes constant-folding for template literals in the minifier by avoiding intermediate String allocations when concatenating template quasi raw/cooked values, instead allocating the final result directly into the arena via atom_from_strs_array.

Changes:

• Replace to_string()/into_string() + concatenation with ctx.ast.atom_from_strs_array([...]) when merging template literal quasis in try_fold_add_op.
• Do the same allocation optimization when inlining constant expressions into template literals in inline_template_literal.

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[codspeed-hq]

Merging this PR will not alter performance

✅ 49 untouched benchmarks
⏩ 7 skipped benchmarks¹

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_{Comparing perf/minifier-template-literal-arena-alloc (0b4228a) with main (e62524d)}

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩