fix: LOW/nit clearance — retier twin dedupe + same-second counter ordering, warn on unknown rotate

- logsetup-2: retier drops a plain file whose .gz twin exists (crash-between-write-and-remove
  residue) up front, so the phantom twin never occupies a retention slot / evicts a real roll.
- logsetup-5: retier breaks mtime ties by the roll counter parsed from the name, so a
  same-second on_start burst tiers newest-first instead of arbitrary listdir order.
- logsetup-3: tiered daily rotator disambiguates an existing dated dest with a counter (no
  clobber on a second same-interval roll).
- logsetup-6: unknown rotate value warns (matching the unknown-output convention) instead of
  silently degrading to a non-rotating file.
- README: size-mode backup naming clarified (numbered flat vs timestamped tiered).
verified stdlib-only; v0.4.0/v0.4.1/size suites still pass. bump v0.4.2 -> v0.4.3

Signed-off-by: disqualifier <dev@disqualifier.me>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "log_setup"
-version = "0.4.2"
+version = "0.4.3"
 description = "stdlib app-entry-point logging setup: live run.log, rotation, gzip, retention, consistent format"
 requires-python = ">=3.10"
 dependencies = []