feat(cast): subscribe to logs using websockets

[bernard-wagner]

Follows on #5571

Motivation

It is useful to monitor for events emitted.

Solution

Introduces: cast subscribe

Building on the introduction of websockets, allow subscribing to events using the same syntax as cast logs.

Some additional changes to_json logic to support streaming.

Moved filter logic from logs.rs to filters.rs to enable reuse.

If --to-block is specified, subscribe to newHeads and exits loop when target block has been reached.

[Evalir]

hey @bernard-wagner just merged #5571 — should be good to continue

[bernard-wagner]

@Evalir open question: Should this be a separate command or should it use a cast logs --subscribe switch?

[Evalir]

hmm i think cast logs --subscribe is good enough @bernard-wagner

[Evalir]

will give a more thorough review later!

[Evalir]

do these docs go here? unsure if they correspond to build_filter

[bernard-wagner]

@Evalir apologies for all the force pushes. Moved to cast logs --subscribe removing the need to move the helper functions out of logs.rs. Improved the docs of the helper functions a bit. Tried passing ctrl-c as general future to Cast, but adds a lot of complexity which seems to be not needed (generic with DefaultType) if Optional.

[Evalir]

lgtm bar failing tests—will rerun them as they seem like spurious network failures