BBPBGLIB-1035 Drop synapse-tool

## Context
E.g. This PR addresses BBPBGLIB-1035 where we kill SynapseTool.

Synapsetool was once the golden bridge to read synapses as it supported multiple formats.

However, with the advent of the SONATA Standard and LibSonata receiving its dedicated reader in Neurodamus `SonataReader` we can now support Sonata Edges without Syntool. Plus, the old NRN files can still be read with the plain-old NrnReader. Therefore basically the Syn2 format gets effectively dropped, which was never really official.

## Scope
 - Kill SynapseReader mod and hoc
 - Drop Python `SynReaderSyntool` and remove any references to it:
    - Auto select now only known about `SonataReader` and `SynReaderNRN`
    - NGV now uses `SonataReader` instead of `SynReaderSyntool`
    - Neuromodulation now uses `SonataReader` instead of `SynReaderSyntool`
 - Make `SonataReader` a bit more flexible for NGV
    - Add the ability to query by source gids
    - wittle optimizations

## Testing
 Whole CI must pass, eventually adapted to drop the few reminiscents of Syn2

## Review
* [x] PR description is complete
* [x] Coding style (imports, function length, New functions, classes or files) are good


Closes BBPBGLIB-1035