asix-sigma: data type nits, minor variable renames

asix-sigma: data type nits, minor variable renames

Address remaining data type nits. Use more appropriate types for sizes
and counters and indices, as well as for booleans.

Prefer more verbose variable names in a few spots to avoid the rather
generic 'i' symbol, especially in complex code paths with deeply nested
flow control or with long distances between declaration and use. Re-use
an existing buffer in the acquisition start for command sequences which
setup trigger in/out as well as clock parameters.

Introduce some variables which may seem unnecessary. But these are
useful for research during maintenance.

This is a mechanical adjustment, behaviour does not change.