Add pipe function to read/write to pipes.

[ghuls]

Add pipe function to read and write to pipes with the help of popen. This allows the following:

$ cat pipe_command_tar.codon
print("Read tar file list")
with pipe("tar tzvf codon-linux-x86_64.tar.gz", "r") as fh:
    i = 0
    for line in fh:
        if i == 15:
            break
        print(line, end="")
        i += 1

print("Gunzip tar file and compress with zstd")
with pipe("gzip -cd codon-linux-x86_64.tar.gz", "r") as in_fh:
    with pipe("zstd -c -9 - > codon-linux-x86_64.tar.zst", "w") as out_fh:
        chunk = in_fh.read(4096*4)
        while chunk:
            out_fh.write(chunk)
            chunk = in_fh.read(4096*4)

$ codon run pipe_command_tar.codon
Read tar file list
drwxr-xr-x root/root         0 2025-11-28 01:00 codon-deploy-linux-x86_64/
drwxr-xr-x root/root         0 2025-11-28 01:49 codon-deploy-linux-x86_64/python/
-rw-r--r-- root/root      2692 2025-11-28 00:32 codon-deploy-linux-x86_64/python/setup.py
-rw-r--r-- root/root        32 2025-11-28 00:32 codon-deploy-linux-x86_64/python/.gitignore
-rw-r--r-- root/root       184 2025-11-28 00:32 codon-deploy-linux-x86_64/python/README.md
-rw-r--r-- root/root        69 2025-11-28 00:32 codon-deploy-linux-x86_64/python/pyproject.toml
drwxr-xr-x root/root         0 2025-11-28 01:00 codon-deploy-linux-x86_64/python/codon/
-rw-r--r-- root/root       134 2025-11-28 00:37 codon-deploy-linux-x86_64/python/codon/version.py
-rw-r--r-- root/root     10317 2025-11-28 00:32 codon-deploy-linux-x86_64/python/codon/decorator.py
-rw-r--r-- root/root      2541 2025-11-28 00:32 codon-deploy-linux-x86_64/python/codon/jit.pyx
-rw-r--r-- root/root       636 2025-11-28 00:32 codon-deploy-linux-x86_64/python/codon/jit.pxd
-rw-r--r-- root/root       279 2025-11-28 00:32 codon-deploy-linux-x86_64/python/codon/__init__.py
-rw-r--r-- root/root        20 2025-11-28 00:32 codon-deploy-linux-x86_64/python/MANIFEST.in
drwxr-xr-x root/root         0 2025-11-28 01:00 codon-deploy-linux-x86_64/python/codon_jit.egg-info/
-rw-r--r-- root/root         6 2025-11-28 01:00 codon-deploy-linux-x86_64/python/codon_jit.egg-info/top_level.txt
Gunzip tar file and compress with zstd

There are a few downsides to using popen:

• popen spawns a shell to execute the "command" and failures of finding the actual command are not 100% reliable to detect. The shell return exit code 127 if if can't find the command and exit code 126 if it is not an executable, but if for some reason the actual command would use the same exit codes, there is no way to communicate that.
• popen only captures stdout and not stderr

So in the long run it is probably better to have a proper implementation that can also capture stderr (and avoids deadlocks when reading both streams) and also captures the real exit code instead of always spawning a shell.