Tests/posix-sysinfo

[Momen-MKadry]

Description of Changes

• Added unit tests for posix-sysinfo library
• Following cases were covered:

Function	Test Case	What It Tests
sysinfo()	sysinfo_no_info	NULL pointer → returns -1
	sysinfo_no_paging	Valid call: verifies all fields (uptime, loads, totalram, freeram, procs, etc.)
	sysinfo_with_paging	Sets total_memory = __UL_MAX, verifies mem_unit, totalram, freeram
fpathconf()	fpathconf	Returns 0 (stub)
pathconf()	pathconf	Returns 0 (stub)
sysconf()	sc_nprocessors_onln	_SC_NPROCESSORS_ONLN → 1
	sc_pagesize	_SC_PAGESIZE → __PAGE_SIZE
	sc_phys_pages	_SC_PHYS_PAGES → total_memory / PAGE_SIZE
	sc_avphys_pages	_SC_AVPHYS_PAGES → free_memory / PAGE_SIZE
	sc_open_max	_SC_OPEN_MAX → MAXFDS or 0
	sc_getpw_r_size_max	_SC_GETPW_R_SIZE_MAX → -1 or 0
	sc_unkown_name	Unknown name → 0 (fallthrough)
confstr()	confstr	Returns 0 (stub)
getpagesize()	getpagesize	Returns __PAGE_SIZE
uname()	uname_null_buf	NULL buffer → returns -1
	uname_valid_buf	Verifies all fields: sysname, nodename, release, version, machine
sethostname()	sethostname_null_name	NULL name → returns -1
	sethostname_too_long_name	Name exceeding nodename size → returns -1
	sethostname_valid_name	Sets "valid-name", verifies via uname(), restores
gethostname()	gethostname_valid_case	Valid buffer → returns 0, matches nodename
	gethostname_buf_too_long	Buffer too small → returns -1, errno == ENAMETOOLONG
getcpu()	getcpu_valid	Both cpu & node non-NULL → set to 0
	getcpu_null_args	Both NULL → returns 0, no crash
	getcpu_partial	Only cpu non-NULL → set to 0

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AI usage note: I used AI mainly to understand existing code and navigate the codebase, and when I finished writing and reviewing the tests I asked for a coverage analysis to make sure nothing was missed and discussed findings with it but nothing was written without understanding it first.

Related Work

N/A

PR Checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran the checkpatch.uk on your commit series before opening this PR;
• Updated relevant documentation.