Switch from Float to Integer Time Values

- Use fast data types where possible so the compiler can optimize for speed based on platform
    - for example, 128 bits might be fastest on ARM
    - good future-proofing

- Refactor GetTimeSinceStart() to be a bit faster
    - multiplication is much faster than division

- Implement a RageTimer method to get the seconds value as a plain int, for the places which cast the seconds value to an int

- Changing from GetTimeSinceStartFast() to GetTimeSinceStart() where accuracy is important

- Changing from GetTimeSinceStart() to GetUsecsSinceStart() for timestamp diffs

- Adjust RageThreads to accomodate an unsigned timestamp value
   - a constant for the maximum value of `uint_fast64_t` replaces `-1` to accommodate the change from signed to unsigned for the `locked_at` variable
   - i have separate constants for `std::numeric_limits<std::uint_fast64_t>::max()` and `static_cast<std::uint_fast64_t>(-1)`, so the reader understands -1 represents an error code, though they evaluate to the same value, so i could remove one of the two

- Add two methods to calculate the MMSSMsMs / MMSSMsMsMs time value from usecs directly instead of inferring it from a seconds value, in RageUtil

- Use a similar counter/modulo based method for WheelNotifyIcon, similar to what i did for text_glow in NoteField in 2eeee03

- Make `g_iStartTime` static const for safety

Rename two timer functions:
GetUsecsSinceStart -> GetTimeSinceStartMicroseconds
GetMicrosecondsSinceStart -> GetSystemTimeAsMicroseconds

Remove std prefix from uint_fast64_t

src/ScreenDebugOverlay.cpp

@@ -1319,7 +1319,7 @@ class DebugLineForceCrash : public IDebugLine
 class DebugLineUptime : public IDebugLine
 {
 	virtual RString GetDisplayTitle() { return UPTIME.GetValue(); }
-	virtual RString GetDisplayValue() { return SecondsToMMSSMsMsMs(RageTimer::GetTimeSinceStart()); }
+	virtual RString GetDisplayValue() { return MicrosecondsToMMSSMsMsMs(RageTimer::GetTimeSinceStartMicroseconds()); }
 	virtual bool IsEnabled() { return false; }
 	virtual void DoAndLog( RString &sMessageOut ) {}
 };