minar::ticks() crashes after 50 days.

Behold this code, in `minar.cpp`:

```
/// convert ticks into the milliseconds time representation
uint32_t minar::ticks(minar::platform::tick_t ticks){
uint64_t milliseconds = ((uint64_t)ticks * 1000U) / minar::platform::Time_Base;
assert(milliseconds <= 0xFFFFFFFF);
return (uint32_t)milliseconds;
}
```

2^32 milliseconds is only 50 days. That is not enough. The easiest fix is to have it return `uint64_t` instead, which gives. 500k years (that is enough). mBed is actually full of timer wrapping issues. It really needs a thorough review.

Start in minar.cpp at minar::ticks(), then inspect its callers before changing the return type. Check how scheduler timing values are consumed and verify behavior beyond 2^32 milliseconds; done means the conversion no longer asserts or truncates at the 50-day limit and the affected code still builds.

Written by the indexing model from the issue text.