fgemm assumes every helper has bounds

[ClementPernet]

All routines in the call tree of fgemm generic wrt the ModeCategory of the base field mention Helper fields such as OutMax, OutMin, Cmin which do not belong to Helpers of ModeCategory::DefaultTag.

As a consequence, the only way to get Givaro::Montgomery<Givaro::ruint<7 > > to work is to assign it a DefaultBoundedTag category although it makes no sense.

Proposed solutions:

1. specialize all fgemm routines on the mode category (to be avoided to reduce code duplication)
2. updated all Outmax,, OutMin fields in if (type_id(modecat) == ) conditions
3. write an updater function, templated by the mode category

[ClementPernet]

Related to #18