perf(lexer): optimize `Source` #25826

Job	Run time
Build Linter Benchmark	2m 46s
Benchmark (lexer)	1m 34s
Benchmark (parser)	1m 48s
Benchmark (transformer)	2m 12s
Benchmark (isolated_declarations)	2m 10s
Benchmark (semantic)	1m 40s
Benchmark (minifier)	2m 12s
Benchmark (codegen)	2m 4s
Benchmark linter (0)	3m 14s
Benchmark linter (1)	1m 35s
Upload benchmarks	22s
	21m 37s

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