Inconsistency in Feed Topic Construction and POD_TOPIC Constant

[IgorShadurin]

The feed topic construction for arbitrary strings in the documentation uses the keccak256 hashing function, as mentioned here: https://github.com/fairDataSociety/FIPs/blob/master/text/0061-personal-storage.md?plain=1#L170

However, in FDP Storage (and thereby in FairOS), the topic is calculated using the BMT Hash of the arbitrary string for every topic.

This introduces additional complexity and computational overhead without any apparent benefit.

Moreover, the POD_TOPIC constant has the value Pods in the library, which is inconsistent with the FIP version PODs.

Expected behavior:

• The feed topic construction should use the keccak256 hashing function as specified in the documentation.
• The POD_TOPIC constant should be consistent with the FIP version.

JS implementation: fairDataSociety/fdp-storage#223