refactor: Remove add_op/node_after and move_after

[acl-cqc]

We only use these in a couple of places, and we never need to - we're always adding after the last sibling of a parent that we have handy anyway.

The _before versions are much more widely used, but maybe we only need one rather than both?

Note this run without the last commit: clippy --all-targets complains that add_op is unused, even though it is used. But it's not that hard to remove...

[aborgna-q]

I don't really see a motivation to drop these. Yes, we mostly only add _before in hugr, but the footprint of this is minimal.

Outside of tests, these are used for manipulating basic blocks where the exit has to be last, or ordering conditional branches. Any of these could have a use for _after at some point.

[acl-cqc]

I don't really see a motivation to drop these. Yes, we mostly only add _before in hugr, but the footprint of this is minimal.

Outside of tests, these are used for manipulating basic blocks where the exit has to be last, or ordering conditional branches. Any of these could have a use for _after at some point.

Yeah, ok, was trying to drain the swamp ;-), but as you say this is only really chipping around the edges, and #622 is much more the right direction; can probably do more after that. Ta :)