feat(pkg-py): Add new QueryChat() API; hard deprecate old API

[cpsievert]

The PR deprecates essentially the entire current (functional) API in favor of a class-based approach (namely QueryChat). The new API looks something like this:

Express

from seaborn import load_dataset
from shiny.express import render, ui
from querychat.express import QueryChat

titanic = load_dataset("titanic")

qc = QueryChat(titanic, "titanic")
qc.sidebar("chat")

with ui.card(fill=True):
    with ui.card_header():
        @render.text
        def title():
            return qc.title() or "Titanic Dataset"

    @render.data_frame
    def data_table():
        return qc.df()

Core

from seaborn import load_dataset
from shiny import App, render, ui
from querychat import QueryChat

titanic = load_dataset("titanic")

qc = QueryChat(titanic, "titanic")

app_ui = ui.page_fluid(
    qc.sidebar(),
    ui.output_data_frame("data_table"),
)

def server(input, output, session):
    qc.server()

    @render.data_frame
    def data_table():
        return qc.df()


app = App(app_ui, server)

Closes #97

TODO

• Update reference/examples/docs (maybe in follow up PR)?

[gadenbuie]

I started reviewing but have talked myself into thinking we should do a clean break API change rather than try to maintain the older functions in a deprecated state. (See #101 (comment))

[gadenbuie]

This is awesome, very excited to see this land! Just a couple of tiny things before merging