[integration][openai] Align default parameters for openai chat model between java and python

[rob-9]

purpose

the Java OpenAI chat model connections (OpenAICompletionsConnection, AzureOpenAIChatModelConnection, and OpenAIResponsesModelConnection) didn't set explicit defaults for timeout and max_retries, falling through to the openai-java SDK's internal values. the Python SDK explicitly defaults to timeout=60s and max_retries=3, meaning the same agent config behaves differently across languages.

this PR aligns Java to match Python:

• adds shared DEFAULT_TIMEOUT_SECONDS = 60 / DEFAULT_MAX_RETRIES = 3 constants in OpenAIChatCompletionsUtils.
• all three Java connections now resolve these via Optional.ofNullable(...).orElse(DEFAULT_*) so absent args get the explicit default.
• invalid values (timeout < 0, retries < 0) throw IllegalArgumentException at construction time instead of being silently skipped.
• javadoc and docs updated to document the new defaults and validation constraints.

testing

• new OpenAICompletionsConnectionTest — asserts correct defaults, explicit overrides, negative rejection, zero acceptance, and api_key validation.
• new OpenAIResponsesModelConnectionTest — same coverage for the Responses API connection.
• extended AzureOpenAIChatModelConnectionTest with default-resolution, override, and boundary assertions.
• new Python test pinning timeout == 60.0 and max_retries == 3.

breaking changes

• max_retries default changed from 2 → 3 for OpenAICompletionsConnection and OpenAIResponsesModelConnection.
• timeout=0 was previously silently ignored (SDK default applied); it is now passed through as Duration.ofSeconds(0).
• negative values for either parameter now throw instead of being silently skipped.

docs

• doc-not-needed

[wenjin272]

Thanks for taking this on @rob-9. The code looks good to me, but I think we should also update the documentation.

The user-facing docs still describe the old Java defaults. After this PR, Java OpenAI/Azure connections explicitly default to timeout=60 and max_retries=3, but these tables still mention SDK fallback/None and max_retries=2. Please update the docs to match the new constructor behavior.

[rob-9]

@wenjin272 thx