tests: add regression test for repeated termreduce printing

tests: add regression test for repeated termreduce printing

Add a regression test that verifies repeated printing of the same
libsmartcols table produces identical output when termreduce is used.

Before the fix, the effective output width would shrink on each print,
resulting in progressively truncated output. The test guards against
future regressions by ensuring printing remains stable across
invocations.

Signed-off-by: Alessandro Ratti <alessandro@0x65c.net>