test: add coverage for spectate, preserve-rooms, infinite-sky, tweak, probe

[Alistair-Afton]

Summary

• Add in-engine regression tests for spectate (status, set with boolean/number/toggle values, error paths), preserve-rooms (feature listing, enable/disable round-trip, unknown-feature errors), infinite-sky (status, help, argument validation), tweak (status map, enable/disable round-trip on eggs-fertile, unknown tweak error), and probe (cursor requirement, tile report, cprobe unit requirement)
• preserve-rooms tests restore persisted feature state via config.wrapper; tweak tests disable any hook they enabled; probe restores the cursor position

Test plan

• Full in-engine suite green: 289/289 tests, 5103/5103 checks (Windows, DF 53.16)
• ci/lint.py clean on all new files