v2.28.6: Tier 3 — collapse dt/ alias

Highlights

refactor(umbrella): collapse dt/ (#265)

scitex.dt is now a literal alias for scitex.datetime — same _LazyModule instance, no extra directory, no duplicate test mirror. Drops dead local copies (dt/_linspace.py, dt/_normalize_timestamp.py) that were unused (the canonical implementations live under datetime/).

scitex.dt is scitex.datetime  # True

Behaviour-preserving: scitex.dt.linspace still resolves to scitex.datetime.linspace. Not deprecated — dt is intentionally a long-term short alias per the existing docs.

Other changes

• ci: rename test-dt.yml → test-datetime.yml to match the surviving directory.

Carryover

• Tier 2 (~30 thin re-export shim dirs → factory pattern) deferred.
• Tier 3 schema/ and module/ deferred (legitimate local logic remaining).