* add NIFS trait abstraction (based on the needs for Nova, Mova, Ova), defining a common interface between the three Nova variants

The recent Ova NIFS PR #163 (https://github.com/privacy-scaling-explorations/sonobe/pull/163)
and Mova NIFS PR #161 (https://github.com/privacy-scaling-explorations/sonobe/pull/161)
PRs add Nova NIFS variants implementations which differ from Nova in the
logic done for the `E` error terms of the instances.

The current Ova implementation (https://github.com/privacy-scaling-explorations/sonobe/pull/163)
is based on the existing Nova NIFS code base and adds the modifications
to the `E` logic on top of it, and thus duplicating the code. Similarly
for the Mova NIFS impl.

The rest of the Mova & Ova schemes logic that is not yet implemented is
pretty similar to Nova one (ie. the IVC logic, the circuits and the
Decider), so ideally that can be done reusing most of the already
existing Nova code without duplicating it. This PR is a first step in
that direction for the existing Ova NIFS code.

This commit adds the NIFS trait abstraction with the idea of allowing to
reduce the amount of duplicated code for the Ova's NIFS impl on top of
the Nova's code.

* add Ova variant on top of the new NIFS trait abstraction

This is done from the existing Ova implementation at
`folding/ova/{mod.rs,nofs.rs}`, but removing when possible code that is not
needed or duplicated from the Nova logic.

* rm old Ova duplicated code

This commit combined with the other ones (add nifs abstraction & port
Ova to the nifs abstraction) allows to effectively get rid of ~400 lines
of code that were duplicated in the Ova NIFS impl from the Nova impl.

* small polishing & rebase to latest `main` branch updates