test: Add comparison of return value for ft_snprintf tests

[itislu]

• Compare ft_printf return value with snprintf instead of hardcoding an expected number.
• Add comparison of return value for ft_snprintf tests
• Add a null buffer test for ft_snprintf

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• Depends on fix: Fix gcc and newer clang compilation #27.

[Copilot]

Pull Request Overview

This PR enhances the test coverage for ft_snprintf by improving return value validation and adding null buffer testing. The changes compare the return values of ft_snprintf against the standard snprintf function instead of using hardcoded expected values, and introduce a new test case for null buffer scenarios.

Key changes:

• Replace hardcoded return value comparisons with dynamic comparison against snprintf return values
• Add comprehensive null buffer test for ft_snprintf
• Update all existing ft_snprintf tests to validate both buffer content and return values

Reviewed Changes

Copilot reviewed 26 out of 26 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
real-tests/ft_snprintf/tests.h	Add declaration for new null_buffer test function
real-tests/ft_snprintf/sourcelist.mk	Include new null buffer test file in build
real-tests/ft_snprintf/07_null_buffer.c	New test validating ft_snprintf behavior with null buffer
real-tests/ft_snprintf/01_string.c to 06_all_features.c	Updated to compare return values with snprintf instead of hardcoded values
real-tests/ft_snprintf/00_launcher.c	Register new null buffer test in test launcher
bonus/real-tests/ft_snprintf/*	Mirror changes for bonus version of tests
bonus/real-tests/ft_printf/*	Update printf tests to use dynamic return value comparison

[itislu]

If you go through it commit by commit, each change should hopefully be self-explanatory.