Use C++ versions of C headers

[derobins]

No description provided.

[Copilot]

Pull request overview

This PR updates system test sources to include the C++ <c*> wrapper headers instead of their C equivalents, aligning the test code with C++-style standard library includes.

Changes:

• Replaced C headers with C++ wrapper headers in system tests (e.g., errno.h → cerrno, string.h → cstring).
• Added some additional C++ wrapper headers in driver.cpp (climits, cstdint, ctime).
• Updated config.cpp to use cstddef instead of stddef.h.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
test/system/driver.cpp	Switches several C headers to C++ wrapper headers (<cerrno>, <climits>, <cstdint>, <ctime>).
test/system/config.cpp	Replaces <stddef.h> with <cstddef>.
test/system/async.cpp	Replaces <assert.h>/<string.h> with <cassert>/<cstring>.

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