Switch to use franklab NwbElectrodeGroup extension

[samuelbray32]

• Fixes #78
  • changes electrode group to be a franklab extension NwbElectrodeGroup object
  • adds additional metadata accepted by this object (targetedlocation, targeted(x,y,z), units)
  • adjusts unit tests
• Resolves #76
  • data now included in the extension object

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (832cb1a) 90.66% compared to head (0c838c4) 90.70%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #79 +/- ## ========================================== + Coverage 90.66% 90.70% +0.03% ========================================== Files 25 25 Lines 2389 2398 +9 ========================================== + Hits 2166 2175 +9 Misses 223 223 ```

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[rly]

Looks good to me!