itsa: Replace fgets(3) with getline(3)

[ac000]

itsa: Replace fgets(3) with getline(3)

getline(3) is generally safer than fgets(3), for example you won't get
truncated input and will always get the \n character.

Rather than using getline(3) directly we create a wrapper function for
it, ssize_t getstdin(char **lineptr);

We don't care about the allocated string size and are always reading
from stdin.

The first thing we do is free(*lineptr) and set it to NULL, this makes
subsequent calls to getstdin() in the same function safe and not leak
memory.

If getline(3) returns an error, we free lineptr and set it to NULL so it
can be safely passed to free by the __cleanup_free function and return
-1. That way we can just check lineptr for NULL to check for an error.

lineptr should always be set to NULL before the first call to getstdin()
in a fucntion.

Signed-off-by: Andrew Clayton <ac@sigsegv.uk>

[Copilot]

Pull request overview

This PR replaces fixed-size fgets(3) stdin reads with a getline(3)-based wrapper (getstdin) to avoid truncated input and simplify interactive prompting across itsa.

Changes:

• Added getstdin(char **lineptr) wrapper around getline(3) for stdin reading.
• Updated multiple interactive prompts to use getstdin() instead of stack buffers + fgets().
• Adjusted related local variables to use __cleanup_free heap strings instead of fixed-size arrays.

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[Copilot]

Pull request overview

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