[Feature Request] Support Patch-style partial reads in WebSocket get_prop()

[CNFeffery]

Is your feature request related to a problem? Please describe.

WebSocket get_prop() already provides a convenient way to read a component property during a callback. It currently returns the complete property value, which works well as a general default.

For large object- or list-shaped props, it could be useful to also support a more flexible partial-read option when only one nested value is needed. For example, a custom button might expose a detailed onClickEvent object, while the callback only needs:

onClickEvent["node1"]["node1-1"]["target"]["value"]

With the current API, the callback retrieves the complete value and then selects this node in Python. An optional client-side path could make this use case more efficient by returning only the requested part.

Describe the solution you'd like

If feasible, it would be helpful for get_prop() to accept an optional partial-read path using the same location types already supported by Dash's Patch: string keys and integer list indices.

For example:

# Nested object value
value = await ws.get_prop(
    "button",
    "onClickEvent",
    path=["node1", "node1-1", "target", "value"],
)

# A list item nested inside an object
record = await ws.get_prop(
    "button",
    "onClickEvent",
    path=["node1", "records", 5],
)

The browser could resolve the path before serialization and return only the selected value or subtree over the WebSocket.

Potential behavior:

• Support nested combinations of string keys and integer indices, matching Patch location semantics.
• Keep the current full-property behavior when path is omitted.
• Preserve the existing asynchronous and timeout behavior.
• Document the behavior for missing keys or invalid indices.

Describe alternatives you've considered

The existing approach of retrieving the complete prop and selecting the value in Python remains straightforward. A clientside callback and a small dcc.Store can also provide similar behavior. A built-in optional path would offer a more concise approach for this use case.

Additional context

• WebSocket callbacks — Reading Props with get_prop
• Partial Property Updates and the Patch class

This could complement the existing get_prop() API with a focused read-side counterpart to Patch: optionally retrieve a nested location without returning the complete property.