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/RageThreads.cpp

@@ -662,7 +662,7 @@ LockMutex::LockMutex( RageMutex &pMutex, const char *file_, int line_ ):
 	mutex( pMutex ),
 	file( file_ ),
 	line( line_ ),
-	locked_at( RageTimer::GetTimeSinceStart() ),
+	locked_at( RageTimer::GetTimeSinceStartMicroseconds() ),
 	locked(false) // ensure it gets locked inside.
 {
 	mutex.Lock();
@@ -682,11 +682,15 @@ void LockMutex::Unlock()
 
 	mutex.Unlock();
 
-	if( file && locked_at != -1 )
+	constexpr uint_fast64_t THRESHOLD_USEC = 15000;
+
+	if (file && locked_at != FAST_ULL_MAX)
 	{
-		const float dur = RageTimer::GetTimeSinceStart() - locked_at;
-		if( dur > 0.015f )
-			LOG->Trace( "Lock at %s:%i took %f", file, line, dur );
+		const uint_fast64_t current_usecs = RageTimer::GetTimeSinceStartMicroseconds();
+		const uint_fast64_t dur_usecs = current_usecs - locked_at;
+
+		if (dur_usecs > THRESHOLD_USEC)
+			LOG->Trace("Lock at %s:%i took %llu microseconds", file, line, dur_usecs);
 	}
 }