Make smallgrp an explicit dependency

[fingolfin]

SEMIGROUPS_ProcessRandomArgsCons for IsReesMatrixSemigroup picks a random group when the caller does not supply one, using NumberSmallGroups and SmallGroup. Without the SmallGrp package this fails, e.g. in a GAP started with `--bare':

gap> RandomSemigroup(IsReesMatrixSemigroup);;
Error, Variable: 'NumberSmallGroups' must have an assigned value

This is the only place in Semigroups using the small groups library.

See gap-system/gap#2434

Co-Authored-By: Claude Opus 5 noreply@anthropic.com

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Of course you could also rework the code to not use SmallGrp, that'd be perfectly cromulent :-)

[fingolfin]

BTW the current function would also run into an error if it happened to produce order equal to one of 1024, 2016, 2024, 2025, 2040 as for those SmallGrp does not provide the groups. So the function is a chance of about 1 in 400 to run into an error.

Also, if the goal was to select small groups uniformly, that is of course also not the case. But I assume you are aware, just wanted to mention it for completeness sake :-).