feat(cargo-codspeed): add internal build mode #159

Performance Regression: -50%

❌ 18 regressed benchmarks
✅ 557 untouched benchmarks

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

	Mode	Benchmark	`BASE`	`HEAD`	Efficiency
❌	WallTime	`Iterative[20]`	20 ns	21 ns	-4.76%
❌	WallTime	`sum_fold`	305 ns	323 ns	-5.57%
❌	WallTime	`Iterative[21]`	21 ns	22 ns	-4.55%
❌	WallTime	`Iterative`	20 ns	21 ns	-4.76%
❌	WallTime	`instant`	10 ns	20 ns	-50%
❌	WallTime	`hamiltonian_cycle[5]`	896 ns	1,655 ns	-45.86%
❌	WallTime	`graph_coloring[6]`	1.1 µs	1.5 µs	-24.62%
❌	WallTime	`string_copy_with_bytes_counter`	61 ns	63 ns	-3.17%
❌	WallTime	`sleep_1ms`	1 ms	1.1 ms	-3.25%
❌	WallTime	`hamiltonian_cycle[6]`	950 ns	1,751 ns	-45.75%
❌	WallTime	`hamiltonian_cycle[7]`	1 µs	1.9 µs	-45.59%
❌	WallTime	`iterative[10]`	16 ns	17 ns	-5.88%
❌	WallTime	`fib_in_thread_bench[30]`	6.8 ms	7.1 ms	-4.25%
❌	WallTime	`fib_in_thread[31]`	10.8 ms	11.2 ms	-3.1%
❌	WallTime	`fib_in_thread_bench_local[31]`	10.8 ms	11.2 ms	-3.09%
❌	WallTime	`fib_in_thread[30]`	6.8 ms	7.1 ms	-4.3%
❌	WallTime	`fib_10`	375 ns	455 ns	-17.58%
❌	WallTime	`fib_in_thread_bench_local[30]`	6.8 ms	7.1 ms	-4.16%

_{Comparing main (693edb3) with main (0afd168)}