Fix broken cross-reference links and raw GitHub URLs in CustomLangChainTracer docstrings

[JimDaly]

Problem

Generated doc page: CustomLangChainTracer Class

The DocFx-generated API page for CustomLangChainTracer in
libraries/microsoft-agents-a365-observability-extensions-langchain/microsoft_agents_a365/observability/extensions/langchain/tracer.py
produces dozens of unresolved cross-reference warnings and contains raw GitHub source URLs that appear as literal links in the published docs.

The warnings and the GitHub URLs fall into two categories with different fixes.

---

Category 1: Google-style type annotation in __init__ docstring (code fix)

The __init__ docstring uses Google-style parenthesised type annotations:

Args:
    tracer (trace_api.Tracer): The OpenTelemetry tracer for creating spans.
    separate_trace_from_runtime_context (bool): ...
    *args (Any): ...
    **kwargs (Any): ...

DocFx extracts the parenthesised strings as type cross-references and generates
<xref:trace_api.Tracer>, <xref:Any>, etc. — none of which it can resolve.

Fix: Remove the parenthesised types from the Google-style format. The types are
already present on the function signature and do not need to be repeated in the
docstring body. The corrected docstring should be:

def __init__(
    self,
    tracer: trace_api.Tracer,
    separate_trace_from_runtime_context: bool,
    *args: Any,
    **kwargs: Any,
) -> None:
    """Initialize the CustomLangChainTracer.

    Args:
        tracer: The OpenTelemetry tracer for creating spans.
        separate_trace_from_runtime_context: When True, always start a new
            trace for each span without a parent, isolating it from any
            existing trace in the runtime context.
        *args: Positional arguments forwarded to BaseTracer.
        **kwargs: Keyword arguments forwarded to BaseTracer.
    """

---

Category 2: Raw GitHub source URLs in on_chat_model_start docstring (code fix)

The on_chat_model_start method docstring contains three raw
https://github.com/langchain-ai/langchain/blob/... URLs. These appear as
literal hyperlinks on the published docs page pointing at LangChain's source
code rather than its API reference, which is confusing for readers.

Fix: Remove the raw GitHub URLs. Replace the docstring with a brief plain-text
explanation of why this override exists, without linking to implementation
internals:

def on_chat_model_start(self, *args: Any, **kwargs: Any) -> Run:
    """Handle chat model start events.

    Delegates to ``LangChainTracer.on_chat_model_start`` to obtain correct
    chat-formatted spans. The ``BaseTracer`` implementation requires setting
    an internal ``_schema_format`` flag; delegating to ``LangChainTracer``
    avoids depending on that private attribute.
    """
    return LangChainTracer.on_chat_model_start(self, *args, **kwargs)  # type: ignore