Add LUA_TINTEGER support for Luau 0.715 compatibility

[Copilot]

Luau 0.715 introduced a new LUA_TINTEGER type for 64-bit integers. The debugger's type system didn't handle it, causing integer64 values to display as "unknown" during debugging.

Changes

• debugger/src/internal/utils/lua_types.h — Add Integer type handler using lua_tointeger64(), register it in RegisteredTypes
• debugger/src/internal/variable.cpp — Handle LUA_TINTEGER table keys in addField so indexed access works correctly for integer64 keys
• .gitignore — Add build-* pattern

class Integer {
 public:
  static constexpr lua_Type type = LUA_TINTEGER;
  static std::string typeName() { return lua_typename(nullptr, type); }
  static std::string toString(lua_State* L, int index) {
    int64_t value = lua_tointeger64(L, index, nullptr);
    return std::format("{}", value);
  }
};

Verified building against Luau 0.715 with both GCC 13 and Clang 18.