lang: for-loop by-ref element capture (for xs: (*x))

(*x) binds x to a pointer into the collection (index_gep) instead of a per-element value copy: passing it on (e.g. to a *T param) is zero-copy and mutations write back. In a value position x auto-derefs — a binary-op operand loads the element, a pointer-typed slot keeps the pointer, and an 'if x == {...}' match derefs the pointee for its tag/payload. Arrays GEP through their storage so writes hit the original. Regression test: examples/for-by-ref-capture.sx.

tests/expected/for-by-ref-capture.exit

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+0

tests/expected/for-by-ref-capture.txt

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+101 102 103
+circle 2.000000
+none