add public api function to retrieve struct tm from time object.
this enables other gems to access time components for formatting
while maintaining encapsulation of internal mrb_time structure.
Co-authored-by: Claude <noreply@anthropic.com>
- `Time.local` and `Time.utc` are able to use with `MRB_INT16 + MRB_WITHOUT_FLOAT`.
- `time_t` is converted directly from the Ruby object.
- `time + sec` and` time - sec` are not affected by the precision of `mrb_float`.
Similarly, calculations are possible with `MRB_INT16 + MRB_WITHOUT_FLOAT`.