Add bounded size limit to _pending_tool_calls dictionary

[Copilot]

The _pending_tool_calls dictionary accumulates tool call IDs without bounds when tool calls are captured but never consumed by matching FunctionSpans. In long-running applications, this causes unbounded memory growth.

Changes

• Added size cap: Introduced _MAX_PENDING_TOOL_CALLS = 1000 constant, matching the pattern used for _MAX_HANDOFFS_IN_FLIGHT
• Converted to OrderedDict: Changed _pending_tool_calls from dict to OrderedDict to enable FIFO eviction
• Implemented eviction logic: Updated capture_tool_call_ids() to enforce max size by removing oldest entries when limit is exceeded

# In OpenAIAgentsTraceProcessor.__init__
self._pending_tool_calls: OrderedDict[str, str] = OrderedDict()

# In capture_tool_call_ids()
pending_tool_calls[key] = call_id
while len(pending_tool_calls) > max_size:
    pending_tool_calls.popitem(last=False)  # Remove oldest

This mirrors the existing bounded approach used for _reverse_handoffs_dict, ensuring consistent memory safety across the trace processor.

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