Fix tests failing with setsid

Following tests are failing when running on a new session started with
setsid command/syscall: pty01, ptem01, setpgid01.

Tihs patch-set refactor them in order to fix this issue. Some tests like
pty01 and ptem01 have been split into multiple files due to their
complexity.

To: [email protected]
Fixes: linux-test-project/kirk#28
Signed-off-by: Andrea Cervesato <[email protected]>

---
Changes in v3:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v2: https://lore.kernel.org/r/[email protected]

Changes in v2:
- add SAFE_PTSNAME macro
- ptem01: check ptsname() with TBROK
- Link to v1: https://lore.kernel.org/r/[email protected]

--- b4-submit-tracking ---
# This section is used internally by b4 prep for tracking purposes.
{
  "series": {
    "revision": 3,
    "change-id": "20241204-fix_setsid_tests-876a46267285",
    "prefixes": [],
    "history": {
      "v1": [
        "[email protected]"
      ],
      "v2": [
        "[email protected]"
      ]
    }
  }
}