SrcFile's debug should not print the whole content

[yihozhang]

Fixes #447

Before:

> RUST_LOG=debug cargo run --release tests/python_array_optimize.egg 2>&1 >/dev/null | wc 
   26609 14906607 220858043

After:

> RUST_LOG=debug cargo run --release tests/python_array_optimize.egg 2>&1 >/dev/null | wc
   26610  788211 10508203

[codspeed-hq]

CodSpeed Performance Report

Merging #449 will degrade performances by 9.09%

_{Comparing fix-debug-print (d9e4ce0) with main (5d637f2)}

Summary

⚡ 3 improvements
❌ 3 regressions
✅ 80 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	fix-debug-print	Change
❌	bool	1.3 ms	1.4 ms	-5.87%
⚡	combined-nested	1,025.1 µs	943.8 µs	+8.61%
⚡	datatypes	589.4 µs	546.7 µs	+7.81%
⚡	delete	645.6 µs	601.5 µs	+7.34%
❌	string	498.4 µs	545.5 µs	-8.63%
❌	string_quotes	432.6 µs	475.9 µs	-9.09%