luavm: new module targeting top 3 Lua VM hotspots (4.5% CPU combined)

Three hooks from perf profiling (34M samples):
- lua_table_get_hash_element (1.65%): prefetch next chain node
- luaS_newlstr (1.35%): hash pre-check before memcmp (Lua 5.0->5.1 fix)
- lua_vm_execute (1.50%): jump table patches for MOVE (MOVDQU),
  ADD/SUB/MUL/DIV (SSE2 replacing x87)

Default off (-Dluavm=true to enable). Arithmetic slow path verified
against disasm: __fastcall(ECX=L, EDX=R(A), stack: opB, opC, tm_id),
callee cleans (RET 0xC).

src/main.zig

@@ -24,6 +24,7 @@ const build_opts = struct {
     const silicon = @import("build_options").enable_silicon;
     const weirdperformance = @import("build_options").enable_weirdperformance;
     const superweirdo = @import("build_options").enable_superweirdo;
+    const luavm = @import("build_options").enable_luavm;
 };
 
 // Conditional module imports
@@ -46,6 +47,7 @@ const ssemaths = if (build_opts.ssemaths) @import("ssemaths/ssemaths.zig") else
 const silicon = if (build_opts.silicon) @import("silicon/silicon.zig") else struct {};
 const weirdperformance = if (build_opts.weirdperformance) @import("weirdperformance/weirdperformance.zig") else struct {};
 const superweirdo = if (build_opts.superweirdo) @import("superweirdo/superweirdo.zig") else struct {};
+const luavm = if (build_opts.luavm) @import("luavm/luavm.zig") else struct {};
 
 const module_active = @import("module_active.zig");
 
@@ -746,6 +748,7 @@ const modules = [_]ModuleHooks{
     if (build_opts.silicon) .{ .name = silicon.module_name, .install = silicon.installHooks, .remove = silicon.removeHooks, .is_active = silicon.isActive } else .{},
     if (build_opts.weirdperformance) .{ .name = weirdperformance.module_name, .install = weirdperformance.installHooks, .remove = weirdperformance.removeHooks, .is_active = weirdperformance.isActive, .remove_on_shutdown = true } else .{},
     if (build_opts.superweirdo) .{ .name = superweirdo.module_name, .install = superweirdo.installHooks, .remove = superweirdo.removeHooks, .is_active = superweirdo.isActive } else .{},
+    if (build_opts.luavm) .{ .name = luavm.module_name, .install = luavm.installHooks, .remove = luavm.removeHooks, .is_active = luavm.isActive } else .{},
 };
 
 fn shutdownDetour() callconv(hook.cc.stdcall) void {