Fix potential matplotlib warning when using ui.line_plot.push

[drkspace]

Description

When trying to use ui.line_plot.push with x or y values that are all equal, you get the following matplotlib warning:

lib/python3.12/site-packages/nicegui/elements/line_plot.py:72: UserWarning: Attempting to set identical low and high ylims makes transformation singular; automatically expanding.
  self.fig.gca().set_ylim(min_y - pad_y, max_y + pad_y)

This PR changes 2 things:

1. It will not update the x and/or y limits if their respective data points are all the same value.
2. Add update_y_lims and update_x_lims parameters to push that will disable the limits updating for that push. This will also allow for custom limits to be set (and not reset every call to push).

Example

This example will have a warning on the current version of nicegui.

from nicegui import ui

lp = ui.line_plot(n=1)

i = 0
def update_lp():
    global i
    lp.push([i], [[0]])
    # lp.push([i], [[0]], update_y_lims=False)

    i += 1
ui.timer(1, update_lp)
ui.run()