feat: add .gitignore to .codspeed folder on creation

[art049]

Summary

• Writes a .gitignore (ignoring everything) into the .codspeed directory when it is first created
• Prevents local benchmark results from being accidentally committed

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will degrade performance by 26.69%

⚡ 14 improved benchmarks
❌ 18 regressed benchmarks
✅ 245 untouched benchmarks

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

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	test_fs_write[10000]	41.9 µs	43.1 µs	-2.91%
❌	WallTime	test_multiprocessing_map[10000]	99.1 ms	113.4 ms	-12.63%
⚡	WallTime	test_make_peak	6.9 µs	6.7 µs	+2.41%
⚡	WallTime	test_hamilton_cycle[graph0]	25.2 µs	23.8 µs	+5.77%
⚡	WallTime	test_match_word_pattern[aba-GraphTreesGraph]	103.1 µs	98.8 µs	+4.33%
⚡	WallTime	test_sudoku[initial_grid0]	8.1 µs	7.9 µs	+2.69%
⚡	WallTime	test_generate_all_combinations[5-4]	11.4 µs	11 µs	+3.66%
⚡	WallTime	test_recursive_fibo_20	5.4 ms	5.3 ms	+2.44%
❌	WallTime	test_sum_of_squares[sum_of_squares_sum_labmda_power]	293.9 µs	335.5 µs	-12.4%
⚡	WallTime	test_multiprocessing_map[1000]	59.2 ms	57.1 ms	+3.74%
⚡	WallTime	test_noop_lambda_decorated	1.4 µs	1.3 µs	+6.37%
❌	WallTime	test_color[graph0-3]	27.6 µs	28.2 µs	-2.41%
⚡	WallTime	test_open_knight_tour[1]	4.2 µs	4.1 µs	+2.12%
❌	WallTime	test_mmap_operation[409600]	128.2 µs	131.5 µs	-2.49%
❌	WallTime	test_array_alloc[100]	1.1 µs	1.2 µs	-2.65%
❌	WallTime	test_is_complete[board0]	1.8 µs	1.9 µs	-3.9%
❌	WallTime	test_mmap_operation[40960]	47.3 µs	48.5 µs	-2.46%
⚡	WallTime	test_noop_pass	512.6 ns	485.8 ns	+5.51%
❌	WallTime	test_minimax[scores0]	7.5 µs	7.7 µs	-3.17%
❌	WallTime	test_multiprocessing_map[100]	53.7 ms	65.2 ms	-17.6%
...	...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.

---

_{Comparing feat/codspeed-gitignore (7c99fca) with master (36f5930)}