fix: Array.from(string) returns string[] without type annotation

[cs01]

Summary

• Array.from("hello") now correctly produces a string[] without needing an explicit type annotation
• Previously, the variable allocator classified the result as i8* (string) instead of %StringArray*, causing garbage values on index access
• Root cause: resolveMethodCallByObjectType returned number[] for all Array.from() calls before the string-aware handler could run

Test plan

• New test fixture arrays/array-from-string.ts
• All existing tests pass
• Self-hosting (Stage 0 + Stage 1) passes

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