Edge kind specific HugrView methods

[ss2165]

Building on from #499, given we have a finite number of edge kinds and restrictions on their use, we should have specific methods for querying those connections. I propose:

    // just value ports
    fn value_ports(&self, node: Node, direction: Direction) -> Self::PortLinks<'_>;
    fn value_neighbours(&self, node: Node, direction: Direction) -> Self::Neighbours<'_>;
    // companion to linked_ports, a linear value port must have one target
    fn linked_liner_port(&self, node: Node, port: Port) -> Option<(Node, Port)>;

    // all Value + Order neighbours
    fn dataflow_neighbours(&self, node: Node, direction: Direction) -> Self::Neighbours<'_>;
    
    fn order_neighbours(&self, node: Node, direction: Direction) -> impl Iterator<Item=Node>;

    // can only be one static input
    fn static_source(&self, node: Node) -> Option<Node>;

    // can be many static targets from one port
    fn static_targets(&self, node: Node) -> impl Iterator<Node>;

    // same as static but for cfg nodes
    fn previous_block(&self, node: Node) -> Option<Node>;
    fn next_blocks(&self, node: Node) -> impl Iterator<Node>;

with these we should be able to minimise/nullify the use of OpType methods like other_edge_kind static_port other_edge_port (so this is also an alternative to #495)