Added missing includes (for uintmax_t, ofstream)

[Teeed]

Platform: arch linux (up-to-date @ 12.02.2024), gcc version 13.2.1 20230801 (GCC)

Fixes following compilation errors:

In file included from src/impl/autotierfs/conflicts.cpp:20:
src/incl/alert.hpp:96:34: error: ‘uintmax_t’ has not been declared
   96 |         std::string format_bytes(uintmax_t bytes) const;
      |                                  ^~~~~~~~~
src/incl/alert.hpp:107:29: error: ‘uintmax_t’ has not been declared
  107 |         double format_bytes(uintmax_t bytes, std::string &unit) const;
      |                             ^~~~~~~~~

and

src/impl/autotierfs/config.cpp:228:25: error: variable ‘std::ofstream f’ has initializer but incomplete type
  228 |         std::ofstream f(config_path.string());