Add Echo/Delay node

[piedoom]

Drafting to track #16 - some things to fix, but I think this is close. Still need to fix issues with pause behavior and time change clicking, as well as smoothing filter values (done). There also may be some performance improvements to be made, especially with how I am handling interpolating between times.

I modeled this after what I presume is happening with Bitwig's delay effect, which allows for both single echos and feedback delays.

                              XFeed In
                                  ▼
                                  │
                                  │             ┌─► XFeed Out
                 ┌──────┐         │   ┌─────┐   │
              ┌─►│Filter├────►────┴──►│Delay├───┤
              │  └──────┘ Feedback    └─────┘   │
              │                               ┌─▼─┐
         In ●─┴──────────────────────────────►│Mix├───► Out
                                              └───┘

Issue criteria:

• mix - The wet/dry mix.
• delay - The amount of delay in seconds
• tap_gain - I found this was redundant with the mix and feedback
• tap lowpass - Renamed to feedback_lpf. I think feedback is more generally understood than tap (and should be more accurate in this case as well).
• tap highpass - Renamed to feedback_hpf for above reason
• enabled - Not needed with mix setting
• Additionally, the node will have a custom Stop event to clear the internal buffers.

Additional features

• Feedback - Transforms this node from a single echo into a delay effect with feedback.
• Multi-channel supports crossfeed feedback
• [🚧] Pause/Unpause

Tradeoffs

• The effect uses its own buffers instead of scratch buffers, as channels above a certain amount may result in more scratch buffers being needed than available.
• For mono versions of the node, crossfeed is still an available parameter, although changing its value does nothing.
• From my initial findings, we may be able to simply crossfade between two delay times, and not do anything fancy like stride interpolation. However, I only tested with sine waves.

[piedoom]

OK, I did some additional testing, and it seems that the issue I was running into where all Notifys are immediately triggered is specific to the UI visual nodes graph example (and it happens with all nodes, and happened before this addition). Can dig in more but technically I think this is an existing "bug". The code itself should be fine

[piedoom]

all of this can use some bikeshedding, idk if these are correct terms

[piedoom]

Added a stereo and mono helper.
I also added some improved documentation that is hopefully more approachable for general developers instead of assuming audio programming knowledge.