EventPrimitives : Add fixed capacity dynamic typedefs. Add test. Fix bug

EventPrimitives :

• Add test for the Amg definitions.
• Fix Eigen assertion on AmgRowVector (seems unused) uncovered by the test.
• Add fixed capacity dynamic typedefs

The last one is a number of dyn allocation vs space trade off.

• There are cases where we know exactly the number and we use the fixed size
• Then there are cases or largish matrices we can not guess the sizes or anyhow quite largish.
• Then there cases we know the max capacity we need (i.e Local Parameters 5 , Measurements covariance 3) even if we do not know the exact number. So it might be interesting to have for these ones where the max is small.

This is like a "small"/ "fixed capacity" vector but for "Eigen"

ping @abarton @smh for the last one