refactor(graphics): cache bytesPerRow in MonochromeBitmap

[adcondev]

Refactored MonochromeBitmap to cache the bytesPerRow calculation in a private field. This removes duplicated calculations in SetPixel, GetPixel, ToImage and GetWidthBytes, improving maintainability and slightly optimizing performance.

Changes:

• Added bytesPerRow field to MonochromeBitmap struct.
• Updated NewMonochromeBitmap to initialize bytesPerRow.
• Updated SetPixel, GetPixel, GetWidthBytes, and ToImage to use the cached bytesPerRow.

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PR created automatically by Jules for task 17139310501292623649 started by @adcondev

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[github-actions]

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[github-actions]

⚡ Benchmark Results

📈 Performance Comparison

📊 Click to expand detailed results

Current Branch Results

BenchmarkNewDocument-4    	1000000000	         0.3120 ns/op	       0 B/op	       0 allocs/op
BenchmarkBuildSimple-4    	 3727083	       324.7 ns/op	     240 B/op	       4 allocs/op
BenchmarkBuildComplex-4   	  429243	      2708 ns/op	    1809 B/op	      25 allocs/op
BenchmarkToJSON-4         	  540000	      2080 ns/op	     592 B/op	       3 allocs/op
BenchmarkParseDocument_Minimal-4    	  516660	      2352 ns/op	     568 B/op	      14 allocs/op
BenchmarkParseDocument_Receipt-4    	   91740	     12619 ns/op	    2392 B/op	      34 allocs/op
BenchmarkCommandUnmarshal_Text-4    	  425286	      2675 ns/op	     568 B/op	      19 allocs/op
BenchmarkCommandUnmarshal_Table-4   	  274526	      4190 ns/op	     944 B/op	      21 allocs/op
BenchmarkTextCommandParsing-4       	  530343	      2106 ns/op	     544 B/op	      16 allocs/op
BenchmarkTableCommandParsing-4      	  239698	      4774 ns/op	    1000 B/op	      29 allocs/op
BenchmarkParseHexString-4           	 7363257	       154.3 ns/op	      48 B/op	       2 allocs/op
BenchmarkCleanHexString-4           	 6494617	       183.6 ns/op	      64 B/op	       2 allocs/op
BenchmarkContainsSequence-4         	295683699	         4.053 ns/op	       0 B/op	       0 allocs/op
BenchmarkCheckCriticalCommands-4    	33236622	        37.28 ns/op	       0 B/op	       0 allocs/op
BenchmarkDocument_Validate-4       	14550812	        82.82 ns/op	       0 B/op	       0 allocs/op
BenchmarkParseDocument_Simple-4    	  498999	      2386 ns/op	     568 B/op	      14 allocs/op
BenchmarkParseDocument_Complex-4   	  139711	      8450 ns/op	    1352 B/op	      26 allocs/op
BenchmarkPrintImage_Small-4             	     612	   1979819 ns/op	 3469938 B/op	      24 allocs/op
BenchmarkPrintImage_Medium-4            	     324	   3673105 ns/op	 5481087 B/op	      24 allocs/op
BenchmarkPrintImage_ThermalPreview-4    	     138	   8734235 ns/op	 5231183 B/op	  230423 allocs/op

Base Branch Results

BenchmarkNewDocument-4    	1000000000	         0.3117 ns/op	       0 B/op	       0 allocs/op
BenchmarkBuildSimple-4    	 3490863	       329.9 ns/op	     240 B/op	       4 allocs/op
BenchmarkBuildComplex-4   	  419557	      2721 ns/op	    1809 B/op	      25 allocs/op
BenchmarkToJSON-4         	  526819	      2111 ns/op	     592 B/op	       3 allocs/op
BenchmarkParseDocument_Minimal-4    	  513639	      2326 ns/op	     568 B/op	      14 allocs/op
BenchmarkParseDocument_Receipt-4    	   92798	     12711 ns/op	    2392 B/op	      34 allocs/op
BenchmarkCommandUnmarshal_Text-4    	  416108	      2728 ns/op	     568 B/op	      19 allocs/op
BenchmarkCommandUnmarshal_Table-4   	  278568	      4162 ns/op	     944 B/op	      21 allocs/op
BenchmarkTextCommandParsing-4       	  518899	      2097 ns/op	     544 B/op	      16 allocs/op
BenchmarkTableCommandParsing-4      	  246740	      4769 ns/op	    1000 B/op	      29 allocs/op
BenchmarkParseHexString-4           	 8633444	       135.2 ns/op	      48 B/op	       2 allocs/op
BenchmarkCleanHexString-4           	 6626664	       182.8 ns/op	      64 B/op	       2 allocs/op
BenchmarkContainsSequence-4         	365941700	         3.248 ns/op	       0 B/op	       0 allocs/op
BenchmarkCheckCriticalCommands-4    	36050787	        34.47 ns/op	       0 B/op	       0 allocs/op
BenchmarkDocument_Validate-4       	14507847	        82.69 ns/op	       0 B/op	       0 allocs/op
BenchmarkParseDocument_Simple-4    	  503178	      2390 ns/op	     568 B/op	      14 allocs/op
BenchmarkParseDocument_Complex-4   	  138735	      8496 ns/op	    1352 B/op	      26 allocs/op
BenchmarkPrintImage_Small-4             	     626	   1922854 ns/op	 3469937 B/op	      24 allocs/op
BenchmarkPrintImage_Medium-4            	     331	   3557589 ns/op	 5481086 B/op	      24 allocs/op
BenchmarkPrintImage_ThermalPreview-4    	     133	   8548054 ns/op	 5231183 B/op	  230423 allocs/op

💡 Note: Use benchstat for statistical comparison

🎯 Summary

• Total Benchmarks: 32
• Average Speed: 2605084 ns/op
• Average Memory: 2396764 B/op
• Average Allocations: 41077 allocs/op

[Copilot]

Pull request overview

This PR refactors the MonochromeBitmap struct to cache the bytesPerRow calculation, eliminating redundant computations and improving code maintainability.

Changes:

• Added a bytesPerRow field to cache the (Width + 7) / 8 calculation
• Updated NewMonochromeBitmap to initialize the cached field
• Modified SetPixel, GetPixel, GetWidthBytes, and ToImage methods to use the cached value instead of recalculating

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