feat: add Windows build support

[art049]

Add conditional compilation for Unix-specific features to enable Windows builds:

• Wrap FIFO-related code with cfg(unix) attributes
• Use platform-specific exit status handling in cargo-codspeed
• Make fifo module Unix-only in lib.rs
• Guard FIFO constants and operations across all crates

This allows the project to build on Windows (build-only, not runtime support).

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #107 will improve performances by 5.15%

_{Comparing feat/windows-build (53c0f95) with fix/windows-build (6f3aa29)}

Summary

⚡ 4 improvements
✅ 163 untouched benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	sleep_100ms	624.4 ns	595.3 ns	+4.9%
⚡	sleep_10ms	595.3 ns	566.1 ns	+5.15%
⚡	sleep_1ms	595.3 ns	566.1 ns	+5.15%
⚡	sleep_50ms	595.3 ns	566.1 ns	+5.15%

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #107 will degrade performances by 46.15%

_{Comparing feat/windows-build (53c0f95) with main (96317b0)}

Summary

⚡ 9 improvements
❌ 14 regressions
✅ 131 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	large_setup	16 ns	12 ns	+33.33%
❌	from_elem[16384]	812 ns	886 ns	-8.35%
⚡	from_elem[4096]	330 ns	316 ns	+4.43%
❌	from_elem[8192]	483 ns	511 ns	-5.48%
⚡	bench_array1[10]	10 ns	9 ns	+11.11%
⚡	bench_array2[10]	10 ns	9 ns	+11.11%
❌	print_env_hello	2.1 µs	2.2 µs	-4.42%
⚡	generate_combinations[6]	1.3 µs	1.3 µs	+4.23%
⚡	generate_parentheses[4]	7.2 µs	6.9 µs	+5.07%
❌	graph_coloring[3]	1 µs	1.1 µs	-7.53%
⚡	hamiltonian_cycle[5]	687 ns	647 ns	+6.18%
⚡	permutations[4]	2.6 µs	2.5 µs	+4.79%
❌	permutations[5]	11.1 µs	13.9 µs	-19.91%
❌	count_set_bits[0]	7 ns	8 ns	-12.5%
❌	count_set_bits[1024]	7 ns	8 ns	-12.5%
❌	count_set_bits[255]	7 ns	8 ns	-12.5%
❌	count_set_bits[42]	7 ns	8 ns	-12.5%
❌	count_set_bits[65535]	7 ns	8 ns	-12.5%
❌	generate_gray_code[1]	143 ns	148 ns	-3.38%
⚡	sleep_100ns	36.5 µs	32.4 µs	+12.6%
...	...	...	...	...

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

[not-matthias]

LGTM.