Decouple physical unit system into an independent package

[komed3]

Move the current physical unit system logic, definitions, and registry from the core schema into a standalone package.

Goals:

• Improve modularity by separating unit management from the schema definitions.
• Enable the unit system to be used as a lightweight dependency in other related projects.
• Standardize unit handling across the @pseinfo ecosystem.

Scope:
Extraction of config/units.ts and related logic into a new repository + npm package.