Fix four bugs: ForIn body dropped, step max error, setLuaVersion case, Lua52 refs

[levno-710]

Summary

Fixes four bugs found in the Prometheus Lua obfuscator codebase:

1. ForInStatement body visits were silently dropped (visitast.lua:142) — visitBlock result was not assigned back to statement.body, causing AST transformations inside for ... in loops to be lost.
2. Step max validation showed wrong value (step.lua:58) — Error message used data.min instead of data.max.
3. Pipeline:setLuaVersion didn't update the Unparser (pipeline.lua:136) — Unparser checks LuaVersion (capital L/V) but setLuaVersion passed luaVersion (lowercase), causing the Unparser to silently fall back to LuaU.
4. Removed references to unsupported Lua52 (SplitStrings.lua) — Replaced LuaVersion.Lua52 with LuaVersion.Lua51.