use math.log10() to find digits in note counts

In 5316b92, I added support for the StepStats side pane in Gameplay to accommodate more than 4 digits of notes.

If the total note count for a song is >= 9999, 4 digits will be used (and leftpadded with 0s as needed), and the display will grow to accommodate extra digits as needed.  For example:

 • "Last Trip" has 22897 notes and needs 5 digits
 • "140 BPM Stamina Killer" has over 100k notes and needs 6 digits
 • "1 week of 100 BPM Stream" has over 4M notes and needs 7 digits

The previous implementation used a while loop, division, and math.pow() to count digits.  This was probably fine since this calculation would only be performed once, prior to Init, but I'd also failed to remember that I needed the same calculation elsewhere in the same file, and was using a very sloppy (number -> string -> number) cast there.

This commit changes both of those to use the more standard math.log10() approach of determining digits in base-10.  It is currently unclear what performance impact this might have, or how I might even assess that.

I still need to handle positioning and zooming of the BitmapText when Center1Player is in effect, but that is a different matter.

BGAnimations/ScreenGameplay underlay/PerPlayer/StepStatistics/JudgmentNumbers.lua

@@ -4,14 +4,11 @@ local possible, rv, pss
 local StepsOrTrail = (GAMESTATE:IsCourseMode() and GAMESTATE:GetCurrentTrail(player)) or GAMESTATE:GetCurrentSteps(player)
 local total_tapnotes = StepsOrTrail:GetRadarValues(player):GetValue( "RadarCategory_Notes" )
 
--- minimum 4 digits for aesthetic reasons
-local digits = 4
--- if total note count is greater than 9999, however, increase digits displayed as needed
-if total_tapnotes > 9999 then
-	while ((total_tapnotes / math.pow(10, digits)) >= 1) do
-		digits = digits + 1
-	end
-end
+-- determine how many digits are needed to express the number of notes in base-10
+local digits = (math.floor(math.log10(total_tapnotes)) + 1)
+-- display a minimum 4 digits for aesthetic reasons
+digits = math.max(4, digits)
+
 -- generate a Lua string pattern that will be used to leftpad with 0s
 local pattern = ("%%0%dd"):format(digits)
 
@@ -64,7 +61,10 @@ for index, window in ipairs(TapNoteScores) do
 				TapNoteJudgments[window] = TapNoteJudgments[window] + 1
 				self:settext( (pattern):format(TapNoteJudgments[window]) )
 
-				leadingZeroAttr = { Length=(digits-tonumber(tostring(TapNoteJudgments[window]):len())), Diffuse=Brightness(SL.JudgmentColors[SL.Global.GameMode][index], 0.35) }
+				leadingZeroAttr = {
+					Length=(digits - (math.floor(math.log10(TapNoteJudgments[window]))+1)),
+					Diffuse=Brightness(SL.JudgmentColors[SL.Global.GameMode][index], 0.35)
+				}
 				self:AddAttribute(0, leadingZeroAttr )
 			end
 		end