Add hard viewport bounds that clamp pan and zoom

[Kastier1]

Problem

An explicit axis domain=(lo, hi) defines the initial visible range, but it does not constrain later interaction. Users can pan the plot completely or partially outside that domain, leaving a chart half-visible or empty.

Disabling pan and zoom entirely addresses static charts (#80), but exploratory charts need a middle ground: allow navigation while preventing the camera from leaving meaningful data bounds.

Reproduction

chart = xy.bar_chart(
    xy.bar(["A", "B", "C"], [10, 20, 30]),
    xy.x_axis(domain=(0, 30)),
)

Plain-drag can move the viewport beyond (0, 30); the domain is treated as an initial view rather than a hard boundary.

Proposed API

Support separate navigation bounds, for example:

xy.x_axis(domain=(0, 30), bounds=(0, 30))
xy.y_axis(bounds="data")

Expected behavior:

• Pan is clamped so the visible window cannot leave the configured bounds.
• Zoom-out is clamped to the maximum bounded extent.
• Zoom-in remains available within the bounds.
• Reversed and log axes preserve their existing semantics.
• domain remains the initial view for backward compatibility.
• bounds=None preserves today's unrestricted navigation.

This is distinct from disabling interaction: it keeps exploratory charts useful without allowing users to lose the data.