Added support for EEGs

[GenFlogi]

Energiegemeinschaft: grid/community consumption split

Adds EEG consumption side support for #310. Supersedes the approach in #343.

What

For Zählpunkte participating in an Energiegemeinschaft (EEG), additionally
import the grid/community consumption split as two new external
statistics, alongside the existing total:

• wnsm:<zp> — unchanged (total consumption, V001/V002)
• wnsm:<zp>_grid — grid draw, role G001 (Restnetzbezug)
• wnsm:<zp>_eeg — supplied by the community, role G003 (Eigendeckung)

G001 + G003 = V002 (per the role mapping established by @tschoerk and
confirmed by @AndiVienna91 in #310). Users wire _grid/_eeg into the
Energy Dashboard as two grid-consumption sources with separate prices.

Auto-detection, no config flow

Participation is detected via the existing
user/zaehlpunkte/{gp}/{zp}/zaehlwerke endpoint: an eagTeilnahmen entry
with status == "A" whose date range covers today. Detection failures are
swallowed to debug — they can never break a normal update.

Testing

• Live-validated against a real EEG account: descriptor matched the main
  ZP (no SmartmeterQueryError), three importers ran, _grid/_eeg
  statistics created, G001 + G003 ≈ V002.
• Only tested with consumption EEG. Sadly don't have access to the flip side
• Only tested with one EEG and haven't tested leaving one

Scope & honest caveats

• Consumption only. Feed-in roles (U001 / E002−U001) deferred —
  issue consensus is solid only on G001/G003; W-M-B's feed-in roles are
  ambiguous (U001 vs U01T).
• OBIS path untouched. find_valid_obis_data is a different
  endpoint/concern; deliberately not modified (minimality).
• Estimated/late-corrected data. EEG values arrive 2 days–weeks late
  and geschaetzt; the incremental importer won't re-pull revised
  values, so the most recent weeks of _grid/_eeg can differ slightly
  from the WN portal. Pre-existing incremental behaviour, more visible
  for EEG.
• Leaving an EEG. Detection cuts on dateTo < today; due to WN's
  data lag the final stretch may never import. A dateTo + grace window
  is a possible future refinement.