Task: Implement Fix the macOS real parse

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(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

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The ORE XML binding and record readers parse reals with ores::platform::numeric::parse_double. They no longer call the floating-point std::from_chars, which libc++ on Apple deletes. Three call sites changed: two in binding.cpp and one in record.cpp. The integer from_chars calls stay. The ores.ore.core.tests suite passes on Linux. Only the macOS job proves the compile fix.