A size that was given but is not one a table can have was corrected in
silence: {"rows": 0} made a table with one row, -1 and 1.5 made the default
four, and 10000 was capped at 500 -- so a script asking for a shape the
command cannot honour got a different table and no indication of it.
A size that is absent still takes the default; a size that is present and
outside the range is refused, naming the key and the range.
Rebased onto the post-split main: `table.insert` moved to
table/structure.rs and the tests to table/sizing.rs. The helper is named
`given` rather than `count`, which that module already imports from
table/target.rs for the repeat count of a row or column insert.
Brandon Thomas