For example,

In a `12 cores` server with `48GB RAM`,
the call to `aggregate_server_key_shares`:
- for `examples/if_and_else`:
  - prior to this commit it took `47.56s`
  - with this commit it takes `4.66s`
- for `examples/non_interactive_fheuint8`:
  - prior to this commit it took `158.15s`
  - with this commit it takes `14.96s`

so about `~10x` reduction.

In a `4 cores` laptop with `8GB RAM` (low capacity laptop, with multiple other apps running    ),
the call to `aggregate_server_key_shares`:
- for `examples/if_and_else`:
  - prior to this commit it took `48.65s`
  - with this commit it takes `23.11s`

so about `~2x` reduction.

Co-authored-by: Carlos Pérez <c.perezbaro@gmail.com>