feat: use_execution_context hook

[jnumainville]

The hook can be used to call code within an execution context

It is a fairly niche hook, but here as an example of it being used to do a table update on a separate thread

import deephaven.ui as ui
import threading
from deephaven.execution_context import get_exec_ctx
from deephaven import agg as agg
import deephaven.pandas as dhpd
import deephaven.plot.express as dx

stocks = dx.data.stocks()

def print_sym(source):
    print(dhpd.to_pandas(source.update(["Symbol = sym"]) \
        .agg_by([agg.avg(cols=["AVG = size"])], by=["Symbol"])))

@ui.component
def exec_ctx_hook(source):

    with_exec_ctx = ui.use_execution_context()
    
    def thread_func():
        #print_sym(source)
        with_exec_ctx(lambda: print_sym(source))

    def start_thread():
        thread = threading.Thread(target=thread_func)
        thread.start()

    ui.use_memo(start_thread, source)

    return None

exec_hook = exec_ctx_hook(stocks)

Fixes #184

[mofojed]

We should be able to memoize this instead:

exec_ctx = use_memo(lambda : exec_ctx if exec_ctx else get_exec_ctx(), [exec_ctx])
exec_fn = use_memo(lambda: partial(func_with_ctx, exec_ctx, [exec_ctx])
return exec_fn