Drop Python 3.12 support

[mavam]

🔍 Problem

• CI still spends coverage on Python 3.12 even though the project can move to a newer supported floor.
• The matrix has redundant include/exclude logic and repeats artifact smoke checks across operating systems.

🛠️ Solution

• Require Python 3.13 or newer and advertise Python 3.13/3.14 support.
• Run the full quality gate on Python 3.13 and compatibility tests on Python 3.14.
• Keep macOS coverage for tests while reducing artifact smoke testing to one Ubuntu job.

💬 Review

• Check whether keeping one macOS Python 3.14 test job is the right balance for path and subprocess behavior.
• Check whether release and publish workflows should continue building on the minimum supported Python version.