test(composer): add PrintLn unit tests

[adcondev]

🎯 What:
Added a new test file pkg/composer/escpos_composer_test.go to test the PrintLn utility function.
This function was previously untested.
A mock mockPrintCapability was created to isolate the test from the actual printer command implementation.

📊 Coverage:

• Added test for successful PrintLn execution (concatenation of Text and LineFeed).
• Added test for error handling when Text command fails.

✨ Result:
Improved test coverage for the composer package and ensured PrintLn behaves as expected.

---

PR created automatically by Jules for task 1340867919024926419 started by @adcondev

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[github-actions]

👋 Thanks for opening this PR, @adcondev!

Here's what will happen next:

• 🤖 Automated checks will run
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• 👀 A maintainer will review your changes

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• ✅ All tests pass
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[github-actions]

⚡ Benchmark Results

📈 Performance Comparison

📊 Click to expand detailed results

Current Branch Results

BenchmarkNewDocument-4    	1000000000	         0.3117 ns/op	       0 B/op	       0 allocs/op
BenchmarkBuildSimple-4    	 3624002	       332.9 ns/op	     240 B/op	       4 allocs/op
BenchmarkBuildComplex-4   	  375037	      2911 ns/op	    1809 B/op	      25 allocs/op
BenchmarkToJSON-4         	  515658	      2150 ns/op	     592 B/op	       3 allocs/op
BenchmarkParseDocument_Minimal-4    	  508786	      2338 ns/op	     568 B/op	      14 allocs/op
BenchmarkParseDocument_Receipt-4    	   92289	     12815 ns/op	    2392 B/op	      34 allocs/op
BenchmarkCommandUnmarshal_Text-4    	  421780	      2817 ns/op	     568 B/op	      19 allocs/op
BenchmarkCommandUnmarshal_Table-4   	  273116	      4225 ns/op	     944 B/op	      21 allocs/op
BenchmarkTextCommandParsing-4       	  513444	      2165 ns/op	     544 B/op	      16 allocs/op
BenchmarkTableCommandParsing-4      	  240529	      4824 ns/op	    1000 B/op	      29 allocs/op
BenchmarkParseHexString-4           	 7577304	       157.8 ns/op	      48 B/op	       2 allocs/op
BenchmarkCleanHexString-4           	 6395600	       195.5 ns/op	      64 B/op	       2 allocs/op
BenchmarkContainsSequence-4         	295085038	         4.056 ns/op	       0 B/op	       0 allocs/op
BenchmarkCheckCriticalCommands-4    	33707640	        35.82 ns/op	       0 B/op	       0 allocs/op
BenchmarkDocument_Validate-4       	14499152	        83.18 ns/op	       0 B/op	       0 allocs/op
BenchmarkParseDocument_Simple-4    	  499314	      2428 ns/op	     568 B/op	      14 allocs/op
BenchmarkParseDocument_Complex-4   	  136674	      8664 ns/op	    1352 B/op	      26 allocs/op
BenchmarkPrintImage_Small-4             	     578	   2043056 ns/op	 3469945 B/op	      24 allocs/op
BenchmarkPrintImage_Medium-4            	     310	   4041344 ns/op	 5481085 B/op	      24 allocs/op
BenchmarkPrintImage_ThermalPreview-4    	     139	   8811963 ns/op	 5231178 B/op	  230423 allocs/op

Base Branch Results

BenchmarkNewDocument-4    	1000000000	         0.3121 ns/op	       0 B/op	       0 allocs/op
BenchmarkBuildSimple-4    	 3641552	       332.1 ns/op	     240 B/op	       4 allocs/op
BenchmarkBuildComplex-4   	  414970	      2919 ns/op	    1809 B/op	      25 allocs/op
BenchmarkToJSON-4         	  534522	      2119 ns/op	     592 B/op	       3 allocs/op
BenchmarkParseDocument_Minimal-4    	  492106	      2334 ns/op	     568 B/op	      14 allocs/op
BenchmarkParseDocument_Receipt-4    	   93241	     12843 ns/op	    2392 B/op	      34 allocs/op
BenchmarkCommandUnmarshal_Text-4    	  414968	      2729 ns/op	     568 B/op	      19 allocs/op
BenchmarkCommandUnmarshal_Table-4   	  269995	      4206 ns/op	     944 B/op	      21 allocs/op
BenchmarkTextCommandParsing-4       	  532665	      2147 ns/op	     544 B/op	      16 allocs/op
BenchmarkTableCommandParsing-4      	  242180	      4810 ns/op	    1000 B/op	      29 allocs/op
BenchmarkParseHexString-4           	 7516606	       160.5 ns/op	      48 B/op	       2 allocs/op
BenchmarkCleanHexString-4           	 6452946	       187.0 ns/op	      64 B/op	       2 allocs/op
BenchmarkContainsSequence-4         	295385060	         4.054 ns/op	       0 B/op	       0 allocs/op
BenchmarkCheckCriticalCommands-4    	32113227	        36.71 ns/op	       0 B/op	       0 allocs/op
BenchmarkDocument_Validate-4       	14496307	        83.01 ns/op	       0 B/op	       0 allocs/op
BenchmarkParseDocument_Simple-4    	  499636	      2422 ns/op	     568 B/op	      14 allocs/op
BenchmarkParseDocument_Complex-4   	  138657	      8613 ns/op	    1352 B/op	      26 allocs/op
BenchmarkPrintImage_Small-4             	     576	   2073029 ns/op	 3469936 B/op	      24 allocs/op
BenchmarkPrintImage_Medium-4            	     314	   3996583 ns/op	 5481085 B/op	      24 allocs/op
BenchmarkPrintImage_ThermalPreview-4    	     136	   8703757 ns/op	 5231180 B/op	  230423 allocs/op

💡 Note: Use benchstat for statistical comparison

🎯 Summary

• Total Benchmarks: 32
• Average Speed: 2743544 ns/op
• Average Memory: 2396764 B/op
• Average Allocations: 41077 allocs/op