Add Patch-style partial reads to WebSocket get_prop

[CNFeffery]

This PR adds optional Patch-style partial reads to WebSocket get_prop().

• Add a keyword-only path argument that accepts string keys and integer list indices, including negative indices.
• Resolve the selected value client-side before WebSocket serialization, while preserving existing full-property reads when path is omitted, None, or [].
• Return None for missing or structurally incompatible locations; reject malformed path arguments before sending a request.
• Add unit and WebSocket integration coverage, and document the API in the architecture guide.

Usage examples

# Existing behavior: read the complete property.
data = await ws.get_prop("store", "data")

# Read a nested object value.
value = await ws.get_prop(
    "store", "data", path=["event", "target", "value"]
)

# Read a list item by its zero-based index.
first_value = await ws.get_prop(
    "store", "data", path=["records", 0, "value"]
)

# Read from a list; negative indices count from the end.
last_value = await ws.get_prop(
    "store", "data", path=["records", -1, "value"]
)

# A string key is not coerced to a list index, so this returns None.
not_found = await ws.get_prop(
    "store", "data", path=["records", "0"]
)
assert not_found is None

# An explicit empty path is also a full-property read.
data = await ws.get_prop("store", "data", path=[])

path accepts string dictionary keys and integer list indices. A returned
None may represent a real null value, a missing location, or a
structurally incompatible path. Object keys must be strings and list indices
must be integers (so "0" is not coerced to 0); malformed path arguments
raise before a request is sent.

Closes #3975

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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