[Contribute] fix: preserve parallel tool call order by index (#291)

[love9rose]

Problem

DashScope returns parallel tool calls each carrying an explicit index. Previously �uildGeneration mapped them to AssistantMessage.ToolCall without preserving that order, so when parallel tool calls arrive as interleaved stream chunks they could be aggregated into the wrong positions downstream.

Fix

• Extracted the ordering into a package-private static helper sortToolCallsByIndex(...) that sorts tool calls by their index (tool calls without an index sort last).
• �uildGeneration now calls this helper before mapping to AssistantMessage.ToolCall.
• Single tool calls are unaffected (sorting is a no-op).

Test

• Added estParallelToolCallIndexOrderPreserved: feeds two tool calls in reversed index order (index=1 before index=0) and asserts they come back ordered by index (get_weather before get_time).
• The test calls the helper directly, avoiding the tool-execution path, so it runs deterministically.

Verification

mvn -pl models/dashscope test -Dtest=DashScopeChatModelTests#testParallelToolCallIndexOrderPreserved -> BUILD SUCCESS.

Related issue: #291

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