Improve following behavior when streaming

[philippjfr]

• Automatically stops following when the user zooms in and starts following when the user resets
• Ensures that if the stream is out-of-sync with the plot the full data is synced

There still appears to be a race condition in bokeh where if a stream event arrives while the frontend is rendering it can cause "backtracking" glitches.

TODO:

• Recompute range based on every new data point
• Fix backtracking (fixed in Panel)

Code

import asyncio
import pandas as pd
import numpy as np

import holoviews as hv
hv.extension('bokeh')

nchannels = 25
buffer = hv.streams.Buffer(data=pd.DataFrame(np.random.randn(10, nchannels).cumsum(axis=1), columns=[chr(65+i) for i in range(nchannels)]))

def out(data):
    return hv.NdOverlay(
        {chr(65+i): hv.Curve(data, 'index', (chr(65+i), 'Amplitude')).opts(subcoordinate_y=True) for i in range(nchannels)}
    )

dmap = hv.DynamicMap(out, streams=[buffer]).opts(legend_position='right', legend_cols=2, responsive=True, min_height=600)

pane = pn.pane.HoloViews(dmap)

async def stream(event):
    for i in range(1, 1000):
        buffer.event(data=pd.DataFrame(np.random.randn(10, nchannels).cumsum(axis=1), columns=[chr(65+i) for i in range(nchannels)], index=np.arange(i*10, i*10+10)))
        await asyncio.sleep(0.01)

pn.Column(pn.widgets.Button(on_click=stream, name='Stream'), pane).servable()

[philippjfr]

The backtracking behavior was fixed in holoviz/panel#7128

[philippjfr]

With range handling:

[codecov]

Codecov Report

Attention: Patch coverage is 76.40449% with 21 lines in your changes missing coverage. Please review.

Project coverage is 88.48%. Comparing base (3b3f10f) to head (62a20ab).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
holoviews/plotting/bokeh/element.py	65.71%	12 Missing ⚠️
holoviews/plotting/bokeh/plot.py	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6318      +/-   ##
==========================================
- Coverage   88.49%   88.48%   -0.02%     
==========================================
  Files         323      323              
  Lines       68304    68431     +127     
==========================================
+ Hits        60448    60550     +102     
- Misses       7856     7881      +25     

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