refactor/pty: manually fork and exec #310

Job	Run time
clippy	1m 33s
lint	46s
check_and_test (ubuntu-24.04, amd64, x86_64-unknown-linux-gnu, x86_64, usr/lib/x86_64-linux-gnu, ...	3m 40s
check_and_test (ubuntu-24.04, amd64, x86_64-unknown-linux-gnu, x86_64, usr/lib/x86_64-linux-gnu, ...	4m 25s
check_and_test (ubuntu-24.04, amd64, x86_64-unknown-linux-gnu, x86_64, usr/lib/x86_64-linux-gnu, ...	5m 14s
check_and_test (ubuntu-24.04, arm64, aarch64-unknown-linux-gnu, aarch64, usr/lib/aarch64-linux-gn...	9m 1s
check_and_test (ubuntu-24.04, arm64, aarch64-unknown-linux-gnu, aarch64, usr/lib/aarch64-linux-gn...	4m 36s
check_and_test (ubuntu-24.04, riscv64, riscv64gc-unknown-linux-gnu, riscv64, usr/lib/riscv64-linu...	5m 20s
check_and_test (ubuntu-24.04, riscv64, riscv64gc-unknown-linux-gnu, riscv64, usr/lib/riscv64-linu...	4m 52s
	39m 27s

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