[os] set_redirect_stdio() cause process hang when child process output large text

[kbkpbot]

Describe the bug

When try to use set_redirect_stdio() get the output of a child process, it will hang when child process try to output large text.

Reproduction Steps

create two file:

sub.v

module main
fn main() {
        // Windows' limit is 4095
        // Linux's limit is 65535
	x := '1'.repeat(65536)    // change to 65535 will not hang under Linux
	println(x)
}

pp.v

module main
import os

fn main() {
	mut p := os.new_process('./sub')
	p.set_redirect_stdio()
	p.wait()
	assert p.code == 0
	output := p.stdout_slurp().trim_space()
	p.close()
	dump(output)
}

then compile files:

v sub.v
v pp.v

run pp

./pp

Expected Behavior

dump the output child:

1111111111111111111111111111111111111111111111....11111

Current Behavior

run ./pp will just hang.

Possible Solution

modify repeat() to a smaller number.
Maybe use a separate thread read the stdout/stderr, before we wait the child finish.

Additional Information/Context

V version

V 0.4.10 21874f9.a9a96b8

Environment details (OS name and version, etc.)

V full version	V 0.4.10 21874f9.a9a96b8
OS	windows, Microsoft Windows 10 企业版 LTSC 19044 64 位
Processor	16 cpus, 64bit, little endian, AMD Ryzen 7 7840H with Radeon 780M Graphics
Memory	1.32GB/27.69GB
V executable	D:\v\v\v\v.exe
V last modified time	2025-03-20 13:20:58
V home dir	OK, value: D:\v\v\v
VMODULES	OK, value: C:\Users\DDT.vmodules
VTMP	OK, value: C:\Users\DDT\AppData\Local\Temp\v_0
Current working dir	OK, value: D:\v\bug\process
Git version	git version 2.43.0.windows.1
V git status	0.4.10-1-ga9a96b89-dirty
.git/config present	true
cc version	N/A
gcc version	N/A
clang version	N/A
msvc version	用于 x64 的 Microsoft (R) C/C++ 优化编译器 19.39.33523 版
tcc version	tcc version 0.9.27 (x86_64 Windows)
tcc git status	thirdparty-windows-amd64 b425ac82
emcc version	N/A
glibc version	N/A

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[huly-for-github]

Connected to Huly®: V_0.6-22383

[phcreery]

Similar: vlang/v-analyzer#130

[kbkpbot]

This can be solved by std_read() before process end:

module main
import os

fn main() {
	mut output := ''
	mut p := os.new_process('./sub.exe')
	p.set_redirect_stdio()
	p.run()
	for p.is_alive() {
		output += p.stdout_read()
	}
	p.wait()
	output += p.stdout_read()
	assert p.code == 0
	p.close()
	dump(output.len)
}

But for windows, it need to implement the function is_pending().