StorageUnit correct efficiency_dispatch/store (counter-proposal 2)

[fneum]

counter proposal 2 for #182

Checklist

• I tested my contribution locally and it seems to work fine.
• [ ] Code and workflow changes are sufficiently documented.
• [ ] Newly introduced dependencies are added to environment.yaml and environment.docs.yaml.
• [ ] Changes in configuration options are added in all of config.default.yaml, config.tutorial.yaml, and test/config.test1.yaml.
• [ ] Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/configuration.rst and doc/tutorial.rst.
• A note for the release notes doc/release_notes.rst is amended in the format of previous release notes.

[fneum]

Also see other counter proposal at #201.

[pz-max]

Thanks for correcting my proposal #182 (found the mistake now through your proposal, thanks 👍).
I like the brilliant use of the lookup_store/dispatch function in this proposal (#202) and hence prefer this version.
Further, with the lookup function the code seems more compact and comprehensible.