feat: change default profile from release to bench for build command

[art049]

Summary

• Changes the default profile for cargo codspeed build from release to bench
• Aligns with standard Rust benchmarking workflow (cargo bench defaults to --profile bench)
• Allows users to leverage bench profile customizations while maintaining compatibility

Test plan

• Verify the change compiles without errors
• Confirm pre-commit hooks pass
• Test that cargo codspeed build now uses bench profile by default
• Ensure existing workflows continue to work with explicit --profile release

Fixes #60

🤖 Generated with Claude Code

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #102 will degrade performances by 8.72%

_{Comparing cod-393-default-to-profile-bench (087f25d) with main (b71c93b)}

Summary

⚡ 2 improvements
❌ 2 regressions
✅ 163 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	recursive[0]	240.3 ns	211.1 ns	+13.82%
⚡	recursive[5]	320.3 ns	291.1 ns	+10.02%
❌	instant	305.3 ns	334.4 ns	-8.72%
❌	system_time	305.3 ns	334.4 ns	-8.72%

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #102 will degrade performances by 71.79%

_{Comparing cod-393-default-to-profile-bench (087f25d) with main (b71c93b)}

Summary

⚡ 10 improvements
❌ 4 regressions
✅ 140 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	large_drop	175.3 µs	167.2 µs	+4.88%
⚡	large_setup	12 ns	11 ns	+9.09%
⚡	from_elem[4096]	338 ns	327 ns	+3.36%
⚡	generate_combinations[5]	827 ns	791 ns	+4.55%
❌	graph_coloring[4]	1 µs	1.1 µs	-3.7%
⚡	permutations[5]	11.4 µs	10.9 µs	+5.19%
❌	permutations[6]	66.6 µs	69.1 µs	-3.63%
⚡	permutations[7]	817 µs	768.8 µs	+6.27%
⚡	add_two_integers[(255, 255)]	20 ns	6 ns	×3.3
⚡	add_two_integers[(42, 13)]	20 ns	6 ns	×3.3
❌	sleep_100ns	16.2 µs	57.6 µs	-71.79%
❌	sleep_100us	126.1 µs	133.6 µs	-5.62%
⚡	sleep_1ns	36.6 µs	23.1 µs	+58.18%
⚡	sleep_1us	36.9 µs	24.5 µs	+50.86%

[GuillaumeLagrange]

thanks @art049 and my new colleague @claude