refactor: centralize and group OBIS codes

[premultiply]

• Move the OBIS codes used across meters into the shared obis package and regroup them by quantity (power / energy / current / voltage).
• Harmonize naming: Import/Export, instantaneous as the unqualified default (OBIS D=7), Demand suffix for the last-average .4.0 registers (D=4), tariff suffix T1/T2 for energy.
• Add VoltageDemand codes (kept here for a follow-up PR that adds HardyBarth phase voltages).

charger/hardybarth-ecb1

• Switch to the renamed shared constants. No functional change.
• Attention: The eCB1 meter API only exposes demand (D=4) and energy (D=8) registers, no instantaneous (D=7) values, so power/current use the Demand variants on purpose (see Hardy Barth eCB1/cPH1/cPH2 #778).

[sourcery-ai]

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[sourcery-ai]

Hey - I've reviewed your changes and they look great!

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